net: add granular lock for the netdev netlink socket

As we move away from rtnl_lock for queue ops, introduce
per-netdev_nl_sock lock.

Signed-off-by: Stanislav Fomichev <sdf@fomichev.me>
Reviewed-by: Mina Almasry <almasrymina@google.com>
Link: https://patch.msgid.link/20250311144026.4154277-3-sdf@fomichev.me


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