pimd: Intelligently drop wrvifwhole packets in some cases

pimd: Intelligently drop wrvifwhole packets in some cases

Suppose we have this

(*,G) IIF = swp1  OIL: swp3
(S,G) IIF = swp2  OIL: swp3 swp4

There exists situations where we can receive the mcast
packet for (S,G) on both swp1 and swp2.  In this case
the packet received on swp1 will be sent from the kernel
to us as a WRVIF and WRVIFWHOLE.

As per normal, WRVIF packet processing handles the assert
case so we know we have not received the packet on a downstream
interface, so no assert.

The WRVIFWHOLE packet processing can then check to see if
it received the packet as a result of the (*,G) mroute
from upstream.  If we have then we can safely drop
the packet.

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