Fix handling of MAD agent registrations with mgmt_class == 0.  In this case
ib_umad should pass a NULL registration request to the MAD core rather than a
request with mgmt_class set to 0.
Signed-off-by: NRoland Dreier <roland@topspin.com>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>