pimd: added comments for upstream and channel_oil new values

pimd: added comments for upstream and channel_oil new values

Added comments which explains the new values for existing fields
and new fields in the upstream and channel_oil data structure.

Following are the summary of the behaviour change in PIM code.

Scenario 1 : RP doesn’t exist/RP not reachable
Event: Join received
Current behaviour:
	No upstream gets created
Changed behaviour:
	Upstream data structure created with below info
	upstream_addr: INADDR_ANY
	channel_oil iif:  MAXVIF
	channel_oil is_valid: FALSE (flag introduced to indicate if this entry is valid to get installed in hardware)
	RPF details: Not valid
	Join state: NOT_JOINED
	Kernal installed: FALSE

Scenario 2: Dummy upstream exists
Event: RP configured
Current Behaviour:
	upstream address updated for the dummy upstream created.
Changed Behaviour:
	upstream_addr: RP address
	channel_oil iif:  MAXVIF
	channel_oil is_valid: FALSE
	RPF details: only RP address updated
	Join state: NOT_JOINED
	Kernel installed: FALSE

Scenario 3: Dummy upstream exists
Event: RP becomes reachable
Current Behaviour:
	Update channel oil, rpf details in the upstream and install in hardware
Changed Behaviour:
	upstream_addr: RP Adress
	channel_oil iif:  MAXVIF
	channel_oil is_valid: FALSE
	RPF details: RPF details updated via NHT callback
	Join state: JOINED
	Kernel installed: TRUE

Scenario 4: MRoute exists
Event: RP gets deleted
Current behaviour:
	Nothing got updated in him upstream and channel oil,
	join timer still runs. Mroute still exists in kernel.
Changed behaviour:
	upstream_addr: INADDR_ANY
	channel_oil iif:  MAXVIF
	channel_oil is_valid: FALSE
	RPF details: Not valid
	Join state: NOT_JOINED (also sent prune towards deleted RPF nbr)
	Kernel installed: FALSE

Scenario 5: MRoute Exists
Event: RP unreachable
Current behaviour:
	Nothing got updated in him upstream and channel oil,
	join timer still runs. Mroute sdeleted from  kernel.
Changed behaviour:
	upstream_addr: RP address
	channel_oil iif:  MAXVIF
	channel_oil is_valid: FALSE
	RPF details: only RP address updated
	Join state: NOT_JOINED (also sent prune towards deleted RPF nbr)
	Kernel installed: FALSE

Scenario 6: Mroute exists
Event: Better RP configured with precise group range & reachable.
Current behaviour:
	No effect on existing route.
Changed behaviour:
	Upstream address: Better RP
	RPF interface: towards the better RP
	Join state: JOINED (Send a prune towards the old RP and send a join
		towards the better RP)

Scenario 7: Mroute exists
Event: RP deleted and another RP with broad group range fits this group & reachable
Current behaviour:
	No effect on current behaviour
Changed behaviour:
	Upstream address: next available RP
	RPF interface: towards the next available RP
	Join state: JOINED (Send a prune towards the old RP and send a join
		towards the better RP)
Signed-off-by: Sarita Patra <saritap@vmware.com>