grgsm_trx: change default TRX port number to 6700

In order to avoid clashes with OsmoTRX, which may be also
running on the same host, let's use a different port range
starting from 6700 by default.

This idea was introduced as a result of OS#2984.

Change-Id: Iaf0c78733bfefcb0b0938abf6d316e27d03ecab4
diff --git a/apps/grgsm_trx b/apps/grgsm_trx
index eafc726..eb7fbdb 100755
--- a/apps/grgsm_trx
+++ b/apps/grgsm_trx
@@ -40,7 +40,7 @@
 class Application:
 	# Application variables
 	remote_addr = "127.0.0.1"
-	base_port = 5700
+	base_port = 6700
 
 	# PHY specific
 	phy_sample_rate = 4 * 1625000 / 6