redhat: watchfrr is built by default, enable it to start at run time

redhat: watchfrr is built by default, enable it to start at run time

watchfrr has become a first class citizen of the FRR system.

Currently it's used to ensure that running daemons stay up and running
as well as to facilitate frr.conf being written.  In the future it is
going to be used to auto-start stop.  As such let's start getting
people to use it now.

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