tests: Fix multicast_pim_bsm_topo2 static route issue

tests: Fix multicast_pim_bsm_topo2 static route issue

API to verify static route was checking whether
router is installed with expected nexthop. In
this particular scenario we has same route as
Connected and Static both. In heavy loaded
system static routes was taking time to get
installed and API was doing the verification
on Connected route instead Static route.
Enhanced scripts to check only static routes.

Issue: https://github.com/FRRouting/frr/issues/11563

Signed-off-by: Kuldeep Kashyap <kashyapk@vmware.com>