bgpd: Always restart timer from scratch in OpenConfirm/Established

bgpd: Always restart timer from scratch in OpenConfirm/Established

Imagine this scenario:

A peer has very large hold/keepalive timers of 600/200.  This peer is
using the DataCenter default time.  As such the open will cause
the t_holdtime to be negotiated to 600 seconds.  Now also imagine
that both peers are in update-delay.  If we do not restart the
timers and both peers are in Update Delay, we will continously
reset the peer because the hold time will be hit( since the peer
is not sending us any data ).

Signed-off-by: Donald Sharp <sharpd@nvidia.com>