introduce encoding/decoding functions for 04.08 CC

this patch implements the encoding/decoding of 04.08 call control information
elements.  It adds new functions to be used for the application interface
patch, and is basis for the application patch (currently patch 36).

Please ignore warnings about unused static functions for now.

(Andreas Eversberg)
diff --git a/openbsc/src/gsm_04_11.c b/openbsc/src/gsm_04_11.c
index c299538..a6f3e7a 100644
--- a/openbsc/src/gsm_04_11.c
+++ b/openbsc/src/gsm_04_11.c
@@ -190,7 +190,7 @@
 	/* mangle first byte to reflect length in bytes, not digits */
 	address_lv[0] = da_len_bytes;
 	/* convert to real number */
-	decode_bcd_number(sms->dest_addr, sizeof(sms->dest_addr), address_lv);
+	decode_bcd_number(sms->dest_addr, sizeof(sms->dest_addr), address_lv, 1);
 
 	smsp += da_len_bytes;