Squashed commit of the following:

    fs/fat:  Resolves issues with truncating the cluster chain when shrinking files via ftruncate().
    fs/fat:  First cut at implementation file shrinkage logic needed to support ftruncate().  Certainly shrinks the file size but it does not appear to correctly disconnect the cluster chains.
    fs/fat:  Restructure some functions in files to better support forthcoming file shrinkage logic.  Put framework for file shrinkage in place.  That logic is incomplete on initial commit.

fs/nxffs: truncate method is implementated in a separate file and should have been in a previous commit.

    fs/nxffs:  Add partial implementation of the truncate method:  It extend files, but cannot yet shrink them.
    fs/smartfs:  Add partial implementation of the truncate method:  It extend files, but cannot yet shrink them.
    fs/fat:  Add partial implementation of the truncate method:  It extend files, but no yet shrink them.
    fs/nfs:  Add support for the truncate method to the NFS file system.

    fs: Add truncate() support for userfs
    fs/unionfs:  Add truncate() support to the unionfs
    fs/tmpfs:  Add ftruncate() support to tmpfs
    syscall/: Add system call support for ftruncate()
    net/route:  Adding ftruncate() support eliminates an issue in file-based routing table management.
    fs:  Add basic framework to support truncate() and ftruncate().  The infrastructure is complete.  Now, however, the actual implementation of ftruncate() will have to be done for each file system.

stm32/chip.h: minor fixes for STM32F334

Approved-by: Gregory Nutt <gnutt@nuttx.org>

net/arp:  Fix IGMP multicast address computation on Nuttx network stack.  This change fixes the IGMP address computation to allow multicast UDP messages. The destination address was created with the incorrect bytes of the given IPv4 address.

arch/arm/src/lpc54xx:  Add some hooks for future 802.1q VLAN support.  configs/lpcxpresso-lpc54628:  Automatically bring up network in the netnsh configuration.

Add FPU to xmc4 ostest

* remove +x from makefiles

* preserve .gdbinit across make clean

* add FPU support to ostest on xmc4

* add FPU test to ostest on xmc4

Approved-by: Gregory Nutt <gnutt@nuttx.org>

arch/arm/src/lpc54xx:  Correct handling of the Ethernet RBU error.  With this fix, Ethernet now appears to be fully functional although still undertested.

arch/arm/src/lpc54xx:  Back out address filtering change in commit 3c65be8c

net:  Fix an error introduced when ICMP and ICMP6 socket support was added in NuttX-7.3.  A gratuitous ARP (or solitication) was being sent after receive of the ECHO replay (advertisement).

arch/arm/src/lpc54xx:  Fix a few more Ethernet issues related to buffer management and address filtering.

arch/arm/src/lpc54xx:  Fix several more issues in bring-up of Ethernet driver.  Still not fully functional.

arch/arm/src/lpc54xx:  Add register level debug output for Ethernet testing.  Fixed a few start up problems.  Still hangs on start-up, however.

arch/arm/src/lpc54xx:  Ethernet. Remove last of #warning issues.  No compiles with no warnings/errors.

arch/arm/src/lpc54xx:  Resolves some design issues with multicast address filtering and also with AVBTP multi-channel operation (the latter design is still incomplete).

arch/arm/src/lpc54xx:  Completes basic packet transfer logic for Ethernet drivers.  Still some unfinished logic for IPv6 multicast logic and for various non-mainstream configurations.  But it is ready for tested.  configs/lpcxpresso-lpc54628:  Add a netnsh configuration that will be used to test the Ethernet driver.  Untested on initial commit.

arch/arm/src/lpc54xx:  Adds basic Ethernet interrupt handling.  Still missing all of the descriptor and packetk buffer handling logic.

arch/arm/src/lpc54xx:  Continuing with Ethernet initializatino logic.  Added MTL initialization and partial MAC initialization.

fs/nfs/nfs_vfsops.c: Fix buffer corruption.  In case multiple read requests to the NFS server are required to fill up the user provided buffer, nfs_read might write behind the end of said buffer.  This is fixed with this change.

arch/arm/src/lpc54xx:  Add (incomplete) Ethernet register definition file.  Add framework for an Ethernet driver.  Initial commit is just the drivers/skeleton.c with naming updated for the LPC54.

arch/arm/src/lpc54xx: Add an RTC driver and a RTC character driver lower half.  configs/lpcxpresso-lpc54628:  Add logic to register the RTC character driver if it is enabled.  Enable the RTC and RTC character driver in the NSH configuration.