geneve: rely on rtnl lock in geneve_offload_rx_ports

geneve: rely on rtnl lock in geneve_offload_rx_ports

udp_tunnel_push_rx_port will grab mutex in the next patch so
we can't use rcu. geneve_offload_rx_ports is called
from geneve_netdevice_event for NETDEV_UDP_TUNNEL_PUSH_INFO and
NETDEV_UDP_TUNNEL_DROP_INFO which both have ASSERT_RTNL.
Entries are added to and removed from the sock_list under rtnl
lock as well (when adding or removing a tunneling device).

Signed-off-by: Stanislav Fomichev <stfomichev@gmail.com>
Reviewed-by: Nikolay Aleksandrov <razor@blackwall.org>
Link: https://patch.msgid.link/20250616162117.287806-2-stfomichev@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>