gprs_ms: Avoid enabling EGPRS if no MCS are supported

This patch avoids enabling EGPRS on MS objects if BTS/VTY assigned no
MCS supported/available for use.
As a result, if NO MCS is enabled/supported EGPRS won't be used despite
the MS announcing through EGPRS MS class that it supports EGPRS.

Change-Id: Ib19e9e006d851c2147de15f4aec36ab65250bdd3
diff --git a/src/tbf.cpp b/src/tbf.cpp
index 4f685e8..2371aed 100644
--- a/src/tbf.cpp
+++ b/src/tbf.cpp
@@ -745,7 +745,7 @@
 	struct gprs_rlcmac_bts *bts_data = bts->bts_data();
 	int rc;
 
-	if (m_ms->egprs_ms_class() > 0)
+	if (m_ms->mode() != GPRS)
 		enable_egprs();
 
 	m_created_ts = time(NULL);