pimd: Add 'show ip mroute fill' command

pimd: Add 'show ip mroute fill' command

When displaying the mroute table, add ability to fill
in all the missing data that for human eyes can be assumed.
This will allow people using grep over the command
can get more information.

sharpd@robot ~> sudo vtysh -c "show ip mroute fill"
Source          Group           Proto  Input      Output     TTL  Uptime
*               229.1.1.1       STATIC dum0       enp3s0     1    00:11:07 Default-IP-Routing-Table
*               229.1.1.1       STATIC dum0       virbr0     1    00:01:47 Default-IP-Routing-Table
sharpd@robot ~>

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