net/smc: increase device refcount for added link group

SMCD link groups belong to certain ISM-devices and SMCR link group
links belong to certain IB-devices. Increase the refcount for
these devices, as long as corresponding link groups exist.

Signed-off-by: Ursula Braun <ubraun@linux.ibm.com>
Signed-off-by: Karsten Graul <kgraul@linux.ibm.com>
Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>