fix compilation of RRH GW
I am not sure this is the correct solution. The problem seems to be that the RRH GW does not use ITTI and thus the type 'as_nas_info_t' is not defined, and then the compilation fails. The simple fix is to include 'as_message.h' in 'openair2/RRC/LITE/defs.h' if ENABLE_ITTI is not defined. Maybe it's not good. RRH GW compiles with this fix.