bgpd: fix various problems with hold/keepalive timers

bgpd: fix various problems with hold/keepalive timers

Problem reported that we weren't adjusting the keepalive timer
correctly when we negotiated a lower hold time learned from a
peer.  While working on this, found we didn't do inheritance
correctly at all.  This fix solves the first problem and also
ensures that the timers are configured correctly based on this
priority order - peer defined > peer-group defined > global config.
This fix also displays the timers as "configured" regardless of
which of the three locations above is used.

Ticket: CM-18408
Signed-off-by: Don Slice <dslice@cumulusnetworks.com>
Reviewed-by: CCR-6807
Testing-performed:  Manual testing successful, fix tested by
submitter, bgp-smoke completed successfully