bgp io counters are inconsistently read (sometimes atomic, sometimes not)

[louberger]

Looking at how update_out is used, it is always set using an atomic operation, but sometimes it is read using atomic_load (bgp_vty.c:7143) and other times not (bgp_show_peer, bgp_snmp.c). It looks like atomic should always be used. Same issue exists for other _out counters incremented in bgp_write.