Fix memory leak in nr_rrc_ue_process_masterCellGroup

- Replace asn1cFreeStruc with ASN_STRUCT_FREE in MAC layer cleanup
- Fixes improper memory management of NR_CellGroupConfig structures

Root cause: asn1cFreeStruc only calls ASN_STRUCT_RESET + free(), which doesn't properly free nested ASN.1 allocations. ASN_STRUCT_FREE frees all nested structures completely.

AddressSanitizer leak trace:
Direct leak of 288 byte(s) in 1 object(s) allocated from:
    /#0 0x7fb72bab4a57 in __interceptor_calloc
    /#1 0x593752b28d0d in SEQUENCE_decode_uper
    /#2 0x593752b9a546 in SET_OF_decode_uper
    /#3 0x593752b2863c in SEQUENCE_decode_uper
    /#4 0x593752b47363 in CHOICE_decode_uper
    /#5 0x593752b2863c in SEQUENCE_decode_uper
    /#6 0x593752b2863c in SEQUENCE_decode_uper
    /#7 0x593752b2863c in SEQUENCE_decode_uper
    /#8 0x593752b2863c in SEQUENCE_decode_uper
    /#9 0x593752b2863c in SEQUENCE_decode_uper
    /#10 0x593752b38551 in uper_decode
    /#11 0x5937527d859f in nr_rrc_ue_process_masterCellGroup
    /#12 0x5937527d9408 in nr_rrc_process_reconfiguration_v1530
    /#13 0x5937527dd5bb in nr_rrc_ue_process_rrcReconfiguration
    /#14 0x5937527f5e6b in nr_rrc_ue_decode_dcch
    /#15 0x5937527ff003 in rrc_nrue
    /#16 0x59375280c6de in rrc_nrue_task

openair2/RRC/NR_UE/L2_interface_ue.c

@@ -140,7 +140,7 @@ void process_msg_rcc_to_mac(nr_mac_rrc_message_t *msg, int instance_id)
       break;
     case NR_MAC_RRC_CONFIG_CG:
       nr_rrc_mac_config_req_cg(instance_id, 0, msg->payload.config_cg.cellGroupConfig, msg->payload.config_cg.UE_NR_Capability);
-      asn1cFreeStruc(asn_DEF_NR_CellGroupConfig, msg->payload.config_cg.cellGroupConfig);
+      ASN_STRUCT_FREE(asn_DEF_NR_CellGroupConfig, msg->payload.config_cg.cellGroupConfig);
       break;
     case NR_MAC_RRC_CONFIG_MIB:
       nr_rrc_mac_config_req_mib(instance_id,