pimd: when node changes from non-DR to DR S,G entry not created

pimd: when node changes from non-DR to DR S,G entry not created

1. When a node changes from non-DR to DR in the given topology,
the node was receiving both PIM Join as well as IGMP join.
Since it was already receiving PIM Join previously, ifchannel was
already present. Hence when it becomes DR, the IGMP source flag is not
set due to issue in the code. Hence it never creates S,G entry thinking
that it is not DR.

2. When pim join expires, the pim flag is not reset when ifchannel is not
deleted.

Issue: #7752

Signed-off-by: Mobashshera Rasool <mrasool@vmware.com>