gobgp: fix rpki cli uptime
gobgp: fix rpki cli uptime

zero uptime means gobgpd never connected to roa server.

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

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