net/smc: Add diagnostic information to smc ib-device

During smc ib-device creation, add network device ifindex to smc
ib-device structure. Register for netdevice changes and update ib-device
accordingly. This is needed for diagnostic purposes.

Signed-off-by: Guvenc Gulce <guvenc@linux.ibm.com>
Signed-off-by: Karsten Graul <kgraul@linux.ibm.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>