net: packet: Do not drop net_pkt immediately

If there are no sockets in the system, then do not drop the
packet immediately as there can be other L2 network handlers
like gPTP in the system. This will also allow ICMP messages
to pass to local handler.

Fixes #34865

Signed-off-by: Jukka Rissanen <jukka.rissanen@linux.intel.com>