net: do not inline netif_tx_lock()/netif_tx_unlock()

These are not fast path, there is no point in inlining them.

Also provide netif_freeze_queues()/netif_unfreeze_queues()
so that we can use them from dev_watchdog() in the following patch.

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