pimd: SGRpt prune received during prune didn't override holdtime

pimd: SGRpt prune received during prune didn't override holdtime

RCA: There were 2 problems.
1. SGRpt prune expiry didn't create S,G entry with none oil when no other
interfaces were part of the oil.
2. When restarting the timer with new hold value, comparision was missing and
old timer was not stopping.

Fix:
SGRpt Prune pending expiry will put SG entry with none oil if no other

Signed-off-by: Saravanan K <saravanank@vmware.com>
interfaces present. If present we will be deleting the inherited oif from oil.
Deleting the oif in that scenario will take care of changing mroute.
When alone interface expires in SGRpt prune pending state, we shall detect by
checking installed flag. if not installed, install mroute.