pimd, pim6d: Don't track nexthop for RP 0.0.0.0 & 0::0

pimd, pim6d: Don't track nexthop for RP 0.0.0.0 & 0::0

Topology:
========
FHR----Source

Problem:
=======
When FHR receives multicast traffic, there is no RP configured,
PIMD does NHT register for RP address 0.0.0.0 and group 224.0.0.0/4
PIM6D does NHT register for RP address 0::0 and group FF00::0/8

frr# show ip pim nexthop
Number of registered addresses: 1
Address         Interface        Nexthop
---------------------------------------------

frr# show ipv6 pim nexthop
Number of registered addresses: 1
Address         Interface        Nexthop
---------------------------------------------

Fix:
====
Dont track nexthop for RP 0.0.0.0 & 0::0.

frr# show ip pim nexthop
Number of registered addresses: 0

frr# show ipv6 pim nexthop
Number of registered addresses: 0

Issue: #12104

Signed-off-by: Sarita Patra <saritap@vmware.com>