bmp: set A flag in Per-Peer Header
bmp: set A flag in Per-Peer Header

Needs to set set A flag in Per-Peer Header if the peer use the legacy
2-byte AS_PATH format.

Signed-off-by: FUJITA Tomonori <93dac1fe9c4b2a3957982200319981492ad4976e@lab.ntt.co.jp>

a16/gobgp,a16/gobgp,osrg/gobgp,a16/gobgp,a16/gobgp,a16/gobgp,osrg/gobgp,tamihiro/gobgp,osrg/gobgp,tamihiro/gobgp,fujita/gobgp,fujita/gobgp,a16/gobgp,tamihiro/gobgp,osrg/gobgp,fujita/gobgp,j-kato/gobgp,tamihiro/gobgp,j-kato/gobgp,a16/gobgp,fujita/gobgp,j-kato/gobgp