Further cleanup: define oai_exit for 4G

The parent commit cleans up and groups oai_exit in one place,
nr-softmodem-common.h. Therefore, this 5G file is included in the 4G
defs_common.h (at least it's mostly 4G), which is not nice. Instead,
define oai_exit also in 4G softmodem-common.h, and include this in
defs_common.h. Remove the cyclic inclusion of defs_common.h in
softmodem-common.h, and resolve all subsequent errors around unknown
types and extern definition mismatches.

nfapi/open-nFAPI/pnf/src/pnf_p7.c

@@ -31,9 +31,7 @@
 
 #define FAPI2_IP_DSCP	0
 
-extern uint16_t sf_ahead;
-
-//uint16_t sf_ahead=4;
+extern int sf_ahead;
 
 void add_slot(uint16_t *frameP, uint16_t *slotP, int offset)
 {