ofproto_v1_[234]_parser: Add notes for vlan_vid match field

To make it possible to refer the usage of vlan_vid match field
at Ryu-documentation, This patch adds notes into ofproto_v1_[234]_parser.

Signed-off-by: IWASE Yusuke <iwase.yusuke0@gmail.com>
Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
ofctl_v1_3: Fix to parse capabilities field in OPFMeterFeatures

Signed-off-by: IWASE Yusuke <iwase.yusuke0@gmail.com>
Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
doc/app/ofctl_rest: Add description for capabilities field in OPFMeterFeatures

Signed-off-by: IWASE Yusuke <iwase.yusuke0@gmail.com>
Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
bgp: support new handler in case of changing BGP session

When BGP session goes up/down, BGPSpeaker can detect changing the session.

Signed-off-by: Toshiki Tsuboi <t.tsubo2000@gmail.com>
Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>