can: add protocol counter for AF_CAN sockets

The third column in the output of the following command:

| # grep CAN /proc/net/protocols

is systematically '0': use sock_prot_inuse_add() to account for the number
of sockets for each protocol on top of AF_CAN family.

Signed-off-by: Davide Caratti <dcaratti@redhat.com>
Link: https://patch.msgid.link/9db5d0e6c11b232ad895885616f1258882a32f61.1741952160.git.dcaratti@redhat.com


Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>