pimd: mtrace router code improvments and fixes

pimd: mtrace router code improvments and fixes

Mtrace router code has been fixed for the case where no PIM
interface exists towards the source and next-hop is returned.

fwd_ttl is set to one, for correct reporting of mcast ttl.

Also, NO_MULTICAST error is returned when there is no PIM.

And prev_hop is set to source, for case when connected to source,
to help termination of hop-by-hop queries.

Dependency of logging on PIM, when sending mtrace packet, has been
removed.

Signed-off-by: Mladen Sablic <mladen.sablic@gmail.com>