pimd: Use correct flag to add an oif

pimd: Use correct flag to add an oif

When we are creating the igmp ifchannel we were creating
it with both a P and a I flag.  This was causing
it to not be cleaned up properly when the interface
was shut down.  Subsuquently when the interface
came back up we would attempt to add it back in
but it would fail.

Ticket: CM-14586
Signed-off-by: Donald Sharp <sharpd@cumulusnetworks.com>