rlc: Rename state() to show_state() to better reflect its function

show_state() is only used for debugging output to make the v(b) array
human readable.
diff --git a/src/rlc.cpp b/src/rlc.cpp
index 99516bb..36320dc 100644
--- a/src/rlc.cpp
+++ b/src/rlc.cpp
@@ -130,7 +130,7 @@
 	return moved;
 }
 
-void gprs_rlc_dl_window::state(char *show_v_b)
+void gprs_rlc_dl_window::show_state(char *show_v_b)
 {
 	int i;
 	uint16_t bsn;
@@ -150,6 +150,8 @@
 		case GPRS_RLC_DL_BSN_NACKED:
 			show_v_b[i] = 'N';
 			break;
+		default:
+			show_v_b[i] = '?';
 		}
 	}
 	show_v_b[i] = '\0';