bugfix: initialize all variables of the 'context' thing
There was a problem in rrc_gNB_process_NGAP_PDUSESSION_RELEASE_COMMAND() where we PROTOCOL_CTXT_SET_BY_INSTANCE() that does not initialize eNB_index leading to a crash later on in pdcp. So let's initialize everything.
Plus, while we're here, use do { } while(0) in the macros, just to avoid problems like:
if (condition) macro;
Without do { } while(0) only the first statement of the macro is done in the if. (Not sure if the code has the problem somewhere, but doesn't hurt to fix.)