convert away from deprecated gsm_7bit_{encode,decode}() functions

which removes yet another bunch of compiler warnings.
diff --git a/openbsc/src/libmsc/gsm_04_08.c b/openbsc/src/libmsc/gsm_04_08.c
index ac1e916..ce87ca0 100644
--- a/openbsc/src/libmsc/gsm_04_08.c
+++ b/openbsc/src/libmsc/gsm_04_08.c
@@ -720,7 +720,7 @@
 		ptr8[2] = 0x80 | name_pad; /* Cell Broadcast DCS, no CI */
 
 		ptr8 = msgb_put(msg, name_len);
-		gsm_7bit_encode(ptr8, net->name_long);
+		gsm_7bit_encode_n(ptr8, name_len, net->name_long, NULL);
 
 	}
 
@@ -748,7 +748,7 @@
 		ptr8[2] = 0x80 | name_pad; /* Cell Broadcast DCS, no CI */
 
 		ptr8 = msgb_put(msg, name_len);
-		gsm_7bit_encode(ptr8, net->name_short);
+		gsm_7bit_encode_n(ptr8, name_len, net->name_short, NULL);
 
 	}