tools: frr-reload.py stop bouncing peers on bfd timer change

tools: frr-reload.py stop bouncing peers on bfd timer change

Problem reported that if a bgp neighbor had a bfd timer change
made in frr.conf and systemctl reload frr performed, the neighbor
with the timer changed bounced.  If the change is made in vtysh
by just adding the new timer values, no peer bounce occurs.  This
fix skips the delete part of the delete/add process in frr-reload
so the peers stay up.

Signed-off-by: Don Slice <dslice@cumulusnetworks.com>