pimd: Fix pim not recognizing itself as an RP in some cases

pimd: Fix pim not recognizing itself as an RP in some cases

During normal course of operations, zebra sends the ZEBRA_INTERFACE_VRF_UPDATE
call up into all connected zclients.  In the case of PIM the
zlookup was expecting a min length of 10, but ZEBRA_INTERFACE_VRF_UPDATE
was sending of size 6.  This min length check makes no sense,
so just remove.

Ticket: CM-16976
Signed-off-by: Donald Sharp <sharpd@cumulusnetworks.com>
Reviewed-by: Daniel Walton <dwalton@cumulusnetworks.com>