net: introduce helper dev_change_tx_queue_len()

net: introduce helper dev_change_tx_queue_len()

This patch promotes the local change_tx_queue_len() to a core
helper function, dev_change_tx_queue_len(), so that rtnetlink
and net-sysfs could share the code. This also prepares for the
following patch.

Note, the -EFAULT in the original code doesn't make sense,
we should propagate the errno from notifiers.

Cc: John Fastabend <[email protected]>
Signed-off-by: Cong Wang <[email protected]>
Signed-off-by: David S. Miller <[email protected]>