IB/usnic: Add UDP support in u*verbs.c, u*main.c and u*util.h

Add supports for:
	1) Parsing the socket file descriptor pass down from userspace.
	2) IP notifiers
	3) Encoding the IP in the GID
	4) Other aux. changes to support UDP

Signed-off-by: Upinder Malhi <umalhi@cisco.com>
Signed-off-by: Roland Dreier <roland@purestorage.com>