ofproto_v1_2_parser: have a default value for push_vlan ethertype

As this would be 0x8100 in most cases, make it the default.

Signed-off-by: YAMAMOTO Takashi <yamamoto@valinux.co.jp>
Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
ofproto_v1_3_parser: have a default value for push_vlan ethertype

As this would be 0x8100 in most cases, make it the default.

Signed-off-by: YAMAMOTO Takashi <yamamoto@valinux.co.jp>
Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>