Fix aerial memory leak
This MR fixes multiple memory leaks detected in the Aerial VNF. The affected messages were the ones received from the PNF into the VNF, as well as the SLOT.response ( vendor-specific from VNF to PNF at end of the slot ) The main leak was related to RX_DATA.indication PDU not being properly copied and freed. This MR fixes the issues reported in #778 (closed)