vty: Add cmd to configure 3g Early Classmark Sending

In state prior to this patch, "3G Early Classmark Sending Restriction"
bit in SI3 rest octets was always set to H, which is a sane default as
the policy to send the information is then controlled by "Early
Classmark Sending Control" bit in the same octet.

However, it seems Quortus SoftCore can have some issues decoding the
option, so let's add a vty cmd to be able to disable it for those
having any issues.

Related: SYS#4021

Change-Id: Ic1afe071038a3bb5871d7ff40f665c8644f801ec
diff --git a/include/osmocom/bsc/gsm_data_shared.h b/include/osmocom/bsc/gsm_data_shared.h
index 240be1c..04669e2 100644
--- a/include/osmocom/bsc/gsm_data_shared.h
+++ b/include/osmocom/bsc/gsm_data_shared.h
@@ -885,6 +885,7 @@
 		} data;
 	} si_common;
 	bool early_classmark_allowed;
+	bool early_classmark_allowed_3g;
 	/* for testing only: Have an infinitely long radio link timeout */
 	bool infinite_radio_link_timeout;