server: fix TERM signal handling
server: fix TERM signal handling

gobgpd should die after sending a notification all the peers in
the established state.

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

YujiOshima/gobgp,tamihiro/gobgp,ishidawataru/gobgp,fujita/gobgp,fujita/gobgp,a16/gobgp,Dipsingh/gobgp,YujiOshima/gobgp,fujita/gobgp,osrg/gobgp,a16/gobgp,a16/gobgp,ramrunner/gobgp,a16/gobgp,Dipsingh/gobgp,a16/gobgp,a16/gobgp,Dipsingh/gobgp,h-naoto/gobgp,j-kato/gobgp,a16/gobgp,ramrunner/gobgp,tamihiro/gobgp,h-naoto/gobgp,YujiOshima/gobgp,fujita/gobgp,tamihiro/gobgp,ishidawataru/gobgp,j-kato/gobgp,tamihiro/gobgp,osrg/gobgp,osrg/gobgp,h-naoto/gobgp,j-kato/gobgp,osrg/gobgp,ramrunner/gobgp,ishidawataru/gobgp