nat: use table ID for nat44 ipfix session events

nat: use table ID for nat44 ipfix session events

Type: fix

IPfix messages about NAT44 session create/delete were being populated
with the FIB table index instead of the table ID. The table ID is the
correct identifier to report externally (NAT64 IPfix messages for BIB
and session create/delete use table ID, as does NAT syslogging). Convert
the table index to an ID before adding it to the IPfix NAT44 session
create/delete message data.

Change-Id: I0166384752b17ff3a8c55aa19fa2af7a8140791e
Signed-off-by: Matthew Smith <mgsmith@netgate.com>