core/lwip: Sample to enable UNDIIF_ID_DEBUG

Requires the following in devel.mk or local.mk:

 CFLAGS += -DLWIP_DEBUG
 CFLAGS  += -DDEBUG=1 -DCORE_DEBUG=1 -DDEBUG_PORT=0x3f8
 GCCWARN += -DDEBUG=1 -DCORE_DEBUG=1 -DDEBUG_PORT=0x3f8

Also quiets malloc() free() __schedule()

Signed-off-by: Gene Cumm <gene.cumm@gmail.com>