pimd: hidden command to set MLAG parameters

pimd: hidden command to set MLAG parameters

The MLAG component on the switch is expected to provide some
properties (such as peerlink-rif) to bootstrap the anycast-VTEP
functionality. The final interface for this is being defined as
a part of the pim-mlag functionality.

This commit provides a hidden command to test the anycast-VTEP
functionality independent of the MLAG component.

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