net: remove dev_base_lock from register_netdevice() and friends.

RTNL already protects writes to dev->reg_state, we no longer need to hold
dev_base_lock to protect the readers.

unlist_netdevice() second argument can be removed.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>