ms: Add support for maximum CS values

Currently the CS values can be increased to CS4 even when the "cs"
configuration command has been used with a lower value. The "cs"
command just sets the initial coding scheme, so other means are
needed to limit the selection. One approach is to use the CS flags
passed in SI, but these are currently ignored.

To make it possible to limit the CS selection by configuring the PCU,
this commit adds the following VTY commands to config-pcu:

- cs max <1-4>             Limit DL and UL CS to the given value
- cs max <1-4> <1-4>       Limit DL and UL CS separately (DL first)
- no cs max                Don't limit

Ticket: #1674
Sponsored-by: On-Waves ehf
diff --git a/src/pcu_main.cpp b/src/pcu_main.cpp
index 2e4a970..cecf786 100644
--- a/src/pcu_main.cpp
+++ b/src/pcu_main.cpp
@@ -176,6 +176,8 @@
 	bts->cs_adj_enabled = 1;
 	bts->cs_adj_upper_limit = 33; /* Decrease CS if the error rate is above */
 	bts->cs_adj_lower_limit = 10; /* Increase CS if the error rate is below */
+	bts->max_cs_ul = 4;
+	bts->max_cs_dl = 4;
 
 	msgb_set_talloc_ctx(tall_pcu_ctx);