net: 8021q: Add pr_fmt

Use the current logging style.

Add #define pr_fmt and remove embedded prefix from formats.

Not converting the current pr_<level> uses to netdev_<level>
because all the output here is nicely prefaced with "8021q: ".

Remove __func__ use from proc registration failure message.

Signed-off-by: Joe Perches <joe@perches.com>
Signed-off-by: David S. Miller <davem@davemloft.net>