[VLAN]: Clean up debugging and printks

- use pr_* functions and common prefix for non-device related messages

- remove VLAN_ printk levels

- kill lots of useless debugging statements

- remove a few unnecessary printks like for double VID registration (already
  returns -EEXIST) and kill of a number of unnecessary checks in
  vlan_proc_{add,rem}_dev() that are already performed by the caller

Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>