Rename static functions from uip_* to something more appropriate.  Globally scoped functions will take more work

SAMA5D4-EK: NSH confuration now has FAT/ROMFS, /dev/zero, /dev/random via TRNG, an NSH startup script, and a RAM disk at /tmp

Move net/uip/uip_checksum.c to net/utils/net_chksum.c; fix missing Make.defs include in net/Makefile