Make sure callbacks being freed are not pending when the
"mlx4_en_deactivate_cq()" function returns.

MFC after:	1 week
Sponsored by:	Mellanox Technologies


git-svn-id: svn+ssh://svn.freebsd.org/base/head@275701 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f