edge: Add max_mcs_ul and max_mcs_dl config

This sets the maximum MCS encoding used for EGPRS RLC data blocks
in either direction.

The following VTY command are added to node config-pcu:

 - mcs max <1-9>         set maximum for both, uplink and downlink
 - mcs max <1-9> <1-9>   set maximum for downlink and uplink (in that
                         order)
 - no mcs max            do not limit

Note that using a value of 4 or below for each direction implies
that a GMSK-only TBF may be assumed, which for instance would allow
the use of the GPRS MS class instead of the possibly more restrictive
EGPRS MS class.

Sponsored-by: On-Waves ehf
diff --git a/src/pcu_main.cpp b/src/pcu_main.cpp
index 77e1082..4156c4b 100644
--- a/src/pcu_main.cpp
+++ b/src/pcu_main.cpp
@@ -179,6 +179,8 @@
 	bts->cs_adj_lower_limit = 10; /* Increase CS if the error rate is below */
 	bts->max_cs_ul = 4;
 	bts->max_cs_dl = 4;
+	bts->max_mcs_ul = 4;
+	bts->max_mcs_dl = 4;
 	/* CS-1 to CS-4 */
 	bts->cs_lqual_ranges[0].low = -256;
 	bts->cs_lqual_ranges[0].high = 6;