Merge pull request #1591 from qlyoung/bgpd-ringbuf

bgpd: use ring buffer for network input

diff --cc bgpd/bgp_fsm.c
Simple merge

diff --cc bgpd/bgp_io.c
Simple merge

diff --cc bgpd/bgpd.c
Simple merge

diff --cc bgpd/bgpd.h
Simple merge