server: don't assume (*api.Path).Nlri is ipv4 NLRI
server: don't assume (*api.Path).Nlri is ipv4 NLRI

use (*api.Path).Family to decide how to decode (*api.Path).Nlri

closes #1185

Signed-off-by: Wataru Ishida <15703620d0b11e835ab4f34ebf88f2f40cce783e@lab.ntt.co.jp>

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