datapath: Use vlan deacceleration function in upcall.

vlan_deaccel_tag() was introduced to move a vlan tag from skb->vlan_tci
to the packet but there was still an open coded variant when doing
an upcall.  vlan_deaccel_tag() also clears skb->vlan_tci which is not
currently done but it makes no difference.

Signed-off-by: Jesse Gross <jesse@nicira.com>
Acked-by: Ben Pfaff <blp@nicira.com>