packet/bgp: Remove binary field of RouteDistinguisher
packet/bgp: Remove binary field of RouteDistinguisher

Keeping binary representation increases the size of structure and can
cause data races.

Signed-off-by: IWASE Yusuke <bb80e84cc9f5a8f01385872ee89032beb5d4eba7@gmail.com>

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