af_packet: allow fanout_add when socket is not RUNNING

af_packet: allow fanout_add when socket is not RUNNING

PACKET socket can retain its fanout membership through link down and up
and leave a fanout while closed regardless of link state.
However, socket was forbidden from joining a fanout while it was not
RUNNING.

This patch allows PACKET socket to join fanout while not RUNNING.

Socket can be RUNNING if it has a specified protocol. Either directly
from packet_create (being implicitly bound to any interface) or following
a successful bind. Socket RUNNING state is switched off if it is bound to
an interface that went down.

Instead of the test for RUNNING, this patch adds a test that socket can
become RUNNING.

Signed-off-by: Gur Stavi <gur.stavi@huawei.com>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Link: https://patch.msgid.link/4f1a3c37dbef980ef044c4d2adf91c76e2eca14b.1728802323.git.gur.stavi@huawei.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>