Fix mismerge in OFED update

When OFED was upgraded to Linux v4.9, a bunch of Linux-specific
netlink changes were dropped. Unfortunately, there was a mismerge
in this process and as a result ib_sa_cancel_query() would fail to
cancel an outstanding MAD.

This was causing rdma_destroy_id() to hang indefinitely waiting
for the MAD to complete and release the final reference.

Sponsored by: Dell Inc.
Differential Revision: https://reviews.freebsd.org/D28421
Reviewed by: hselasky, kib
MFC after: 2 months