vlan: Remove unnecessary comparison of unsigned against 0

args.u.name_type is of type unsigned int and is always >= 0.

This fixes the following GCC warning:

  net/8021q/vlan.c: In function ‘vlan_ioctl_handler’:
  net/8021q/vlan.c:574:14: warning: comparison of unsigned expression >= 0 is always true [-Wtype-limits]

Signed-off-by: Tobias Klauser <tklauser@distanz.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>