libfrr: Retain ret value if the best idx is found

libfrr: Retain ret value if the best idx is found

While iteratively looking for a best match route-map index amongst
a list of potential best match route-map indices, if a candidate
best match index is already found, disregard the value returned by
the function route_map_apply_match() if it returns either RMAP_NOOP
or RMAP_NOMATCH in the following iterations.
This is because if a best match route-map index is found then, the
return value must always be set to RMAP_MATCH.

Signed-off-by: NaveenThanikachalam <nthanikachal@vmware.com>