server: handle closed passiveConnCh channel
server: handle closed passiveConnCh channel

When a peer is deleted, passiveConnCh is closed implicitly.

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

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