IB/mlx4: Add and improve logging

Add missing check for success after call to mlx4_ib_send_to_wire() in
mlx4_ib_multiplex_mad().

Amended the existing pr_debug() in mlx4_ib_multiplex_cm_handler() and
mlx4_ib_demux_cm_handler() with attr_id during a lookup failure.

Removed two noisy pr_debug() in mad.c

Fixes: 3cf69cc8 ("IB/mlx4: Add CM paravirtualization")
Link: https://lore.kernel.org/r/20200803061941.1139994-2-haakon.bugge@oracle.com


Signed-off-by: Håkon Bugge <haakon.bugge@oracle.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>