net: use hlist_for_each_entry()

Small cleanup of __dev_get_by_name() and __dev_get_by_index()
to use hlist_for_each_entry() : They'll look like their _rcu variant.

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>