[PATCH] IB: Fix pack/unpack when size_bits == 64

Fix handling of fields with size_bits == 64.  Pointed out by Hal Rosenstock.

Signed-off-by: Roland Dreier <rolandd@cisco.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>