pimd: MUTE flag to suppress traffic forwarding on non-DF

pimd: MUTE flag to suppress traffic forwarding on non-DF

If an mroute loses DF election (with the MLAG peer) it has to stop
forwarding traffic on active-active devices such as ipmr-lo used
for vxlan traffic termination. To acheive that this commit
introduces a concept of OIF muting. That way we can let the PIM and
IGMP state machines play out and silence OIFs after the fact.

Relevant outputs:
=================
1. muted OIFs are displayed with the M flag in "pim state" -
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
root@TORC12:~# net show pim state |grep "27.0.0.13"|grep 100
1         27.0.0.13        239.1.1.100      uplink-1          ipmr-lo(   *M)
root@TORC12:~#
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
2. And supressed altogether in the mroute output -
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
root@TORC12:~# net show mroute |grep "27.0.0.13"|grep 100
27.0.0.13       239.1.1.100     none   uplink-1         none             0    --:--:--
root@TORC12:~#
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

Signed-off-by: Anuradha Karuppiah <anuradhak@cumulusnetworks.com>