gprs_ns2: set default dialect to ipaccess

The default pcu dialect is ipaccess. Keep it that way.

Fixes ttcn3 pcu testcases.

Change-Id: I426f507fb8863abd8995bc615dc6a6fa7ae69217
diff --git a/src/bts.cpp b/src/bts.cpp
index 1376686..b4f902a 100644
--- a/src/bts.cpp
+++ b/src/bts.cpp
@@ -254,6 +254,7 @@
 	bts->mcs_lqual_ranges[8].low = 23;
 	bts->mcs_lqual_ranges[8].high = 256;
 	bts->cs_downgrade_threshold = 200;
+	bts->ns_dialect = NS2_DIALECT_IPACCESS;
 
 	/* TODO: increase them when CRBB decoding is implemented */
 	bts->ws_base = 64;