[GPRS] Change SI13 to NMO_II, as some phones (like G1) dislike NMO_III

I still believe NMO_III is what we want, but as indiciated some phones
absolutely refuse to even connect to the GPRS network in this mode :(
diff --git a/openbsc/src/system_information.c b/openbsc/src/system_information.c
index 6e18079..eb4ac7c 100644
--- a/openbsc/src/system_information.c
+++ b/openbsc/src/system_information.c
@@ -397,7 +397,7 @@
 
 static struct gsm48_si13_info si13_default = {
 	.cell_opts = {
-		.nmo 		= GPRS_NMO_III,
+		.nmo 		= GPRS_NMO_II,
 		.t3168		= 2000,
 		.t3192		= 200,
 		.drx_timer_max	= 3,