net: 8021q: skip packets if the vlan is down

If the vlan is down, free the packet instead of proceeding with other
processing, or counting it as received.  If vlan interfaces are used
as slaves for bonding, with arp monitoring for connectivity, if the rx
counter is seen to be incrementing, then the bond device will not
observe that the interface is down.

CC: David S. Miller <davem@davemloft.net>
Signed-off-by: Vishakha Narvekar <Vishakha.Narvekar@dell.com>
Signed-off-by: David S. Miller <davem@davemloft.net>