Prevent the PNF from sending P7 messages after sending a STOP.indication
Upon stopping the PNF, when sending the STOP.indication to the VNF, set
pnf_p7->terminate to 1.
Add a check on the PNF P7 send functions to not send a message after
pnf_p7->terminate is set.
This prevents the PNF from sending SLOT.indications after stopping,
which sometimes was causing the VNF to process a SLOT.indication after
it had received the indication to STOP.
Also, this MR adds a sanity check on the VNF P7 message handler to
ignore any P7 messages it receives after having it's own terminate flag
set to 1
This MR closes issue #1045