IP forwarding: Move to separate directory. A few fixes from early testing; In TUN driver, do all polling on worker thread.  Otherwise, the stack gets very deep.

IP forwarding: A few fixes from early testing; In TUN driver, do all polling on worker thread.  Otherwise, the stack gets very deep.

Move TUN ioctl commnd to include/nuttx/net/ioctl.h so that it will always be unique.  It a error in netdev_register: it was not handling device names properly when TUN is the only network device.

network:  Correct some issues that prevent TCP from working correctly when both IPv4 and IPv6 are enabled.

IP forwarding design simplication; might save some memory.  Also fix some compile issues introduce with last commit in MULTINIC configration.

configs/Board.mk:  Remove quotes from CONFIG_ARCH_FAMILY.  Causes problems with Windows native build.

STM32 Kconfig: 'unfold' some of the dependencies to provide better long term configuration support.  This also effective reverts the recent 15b85738

Rename CONFIG_STM32_STM32F40XX to CONFIG_STM32_STM32FXXXX since it is used by F4 parts other than F40x

In arch/arm/src/stm32/Kconfig when the CPU is a STM32F4, some STM32_HAVE_xx with xx = {OTGFS, TIM3, TIM4, SPI3, I2S3, I2C3} are selected by default. But for F410 these peripherals are absent. This change add tests to check if the target CPU is an F410 or not and selects according to the situation.  This also adds a select for STM32_HAVE_DAC1 present on this STM32 flavor.

FS: Remove DEBUGASSERT() in block_proxy() because the flags are cleared later.

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

IP Forwarding: Add IPv4 packet forwarding logic.  Initial commit is an untested clone of the IPv6 forwarding logic with a few minor logic changes for IPv4.

IP Forwarding: Add IPv4 packet forwarding logic.  Initial commit is an untested clone of the IPv6 forwarding logic with a few minor logic changes for IPv4.

IP forwarding: In check it the Ethernet MAC address is in the ARP/Neighbor table, add an additional check to skip in the case of CONFIG_NET_MULTILINK and the devices is not an Ethernet device.

configs/Board.mk:  Remove comment form end of line. In windows native build, it appears to be trying to make that an extra parameter to the AR command

I've found that the interrupts aren't enabled since nothing updates them after btn_poll() marks the file descriptor structure as being polling. I've managed to make it work with this change.

UDP networking:  The TTL (time to live) was not being set in the IPv4 or IPv6 header unless the UDP socket was bound.

IP forwarding.  Adds a little more structure to handle passing packets received on one network device to another network device.  Logic is still incomplete.