pimd: add support for configuring multicast static routes

pimd: add support for configuring multicast static routes

Hi,

This patch adds the ability to configure multicast static routes
directly into pimd. Two source files are introduced to implement the new
feature in addition to changes to existing files.

Here is how it can be used the CLI:

interface <incoming interface>
ip mroute <outgoing interface> <group addr>                          #
for asm
or ip mroute <outgoing interface> <group addr> <source>    # for ssm

Please let me know if you have any questions or concerns,

Regards,
Jafar

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