vxlan: drop sock_lock

We won't be able to sleep soon in vxlan_offload_rx_ports and won't be
able to grab sock_lock. Instead of having separate spinlock to
manage sockets, rely on rtnl lock. This is similar to how geneve
manages its sockets.

Signed-off-by: Stanislav Fomichev <stfomichev@gmail.com>
Reviewed-by: Ido Schimmel <idosch@nvidia.com>
Reviewed-by: Nikolay Aleksandrov <razor@blackwall.org>
Link: https://patch.msgid.link/20250616162117.287806-3-stfomichev@gmail.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>