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.

stm32f429i-disco, stm3240g-eval, stm3220g-eval, stm3210e-eval:  Eliminate duplicate Make.defs files.

Build System:  It is no longer necessary to have a unique Make.defs file for each configuration.  A board may share a common Make.defs file in the scripts directory.

ipforward.h:  Add some forward references that are needed when CONFIG_NETDEV_MULTINIC is not enabled.

Fix some errors in ipforward.h when CONFIG_NET_STATISTICS is enabled, but CONFIG_NETDEV_MULTINIC is not