pimd: Carefully Reconstruct FHR state when interface bounces

pimd: Carefully Reconstruct FHR state when interface bounces

When an interface bounces and we receive a packet before
pim has a chance to fully bring the 'struct pim_usptream'
back up correctly, first check to see if we already have
an associated data structure before creating it again.

This removes a case where both the c_oil and up ref counts
were being incremented and never removed properly.

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