Bug 1212: Values of VLAN match fields were wrong.

Values of match fields for VLAN tag were wrong when used AD-SAL OF
plugin and tried to create a flow entry which matched packets without
VLAN tags. V6Match class of AD-SAL OF plugin didn't have code for
handling packets without VLAN tags.

Changes:
 * Added code for handling packets without VLAN tags to V6Match class.
 * Added test cases related to the change of V6Match class.

Change-Id: Ic9c3a6c47c7e99d5273e48ec2ed8d0399289cddb
Signed-off-by: Hideyuki Tai <h-tai@cd.jp.nec.com>