Add ghost parameter to processPkt and its dependencies

[LinoTelschow]

As is:

• at the moment the processPkt method doesn't return information if the processResult contains an SCMP error packet.

To Be:

• the processPkt method should have a postconditon like:

isSCMPError ==> !isEmptyPR(result)

ghost
ensures res == (pr.EgressID == 0 && pr.OutConn == nil && pr.OutAddr == nil && pr.OutPkt == nil && pr.AddrSrc == 0)
decreases
pure func isEmptyPR(pr processResult) (res bool) {
	return pr.EgressID == 0 && pr.OutConn == nil && pr.OutAddr == nil && pr.OutPkt == nil && pr.AddrSrc == 0
}

With this information the caller of processPkt could deduce that processResult is not empty.