Composite:  Move board_msc* interfaces from apps/system/composite to the board specific OS logic where they belong.

Socket I/F: More fixes for USRSOCK.  The good link fooled me because a critical file was not included in the link.

Socket I/F: Fix bad copy-past error.  sendto() was called the address family's send() instead of sendto().

Socket interface:  Fix some configuration chaos.  Sometime CONFIG_NET_UDP/TCP was used when CONFIG_NET_LOCAL_DGRAM/STREAM was intended.

STM32 F7 Ethernet:  Fix typo in header; Add memory sync barrier between writing to DMA TX descriptor and restarting DMA TX. Avoid calling work_queue on pollwork if it's already queued, just skip a poll cycle instead.  Nucleo-144: Fix RMII TXD1 signal, connected to PB13 not to PG14.

Sockets:  Initial steps to adde a socket interface to the networking.  Each address family will have an interface that describes how to perform socket operations on that address family.  Currently only a couple of methods are defined in the table as a proof of concept.  More to come.  Currently there are only tables for the INET/INET6 family, the Unix LOCAL family, and the raw PACKET family.  Hopefully there will be AF_IEEE802154 and AF_BLUETOOTH comming down the pike.

I was having issues with the bus freezing up .. slaves holding SDL low.. so I rewrote a good portion of the interrupt logic based on the application notes from Atmel.  One major improvement is using the RXNACK flag in the STATUS register, which indicates that no device responded to an address packet. Assuming that the chip will always give an interrupt status, I believe it's possible to eliminate the timer as well.