server: fix deadlock regression
server: fix deadlock regression

introduced by 433440067d8084556a31ffd4b8bfa8671bfcaab2

Reported-by: Eiichiro Watanabe <519567a6eb7a7ef4792411380c825be940da80e8@gmail.com>
Signed-off-by: FUJITA Tomonori <93dac1fe9c4b2a3957982200319981492ad4976e@lab.ntt.co.jp>

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