[l2] Do not always release the layer2 when closing the socket (Andreas Eversberg)

Tells mISDN not to release layer 2 on closing socket, when not
requested. If mISDN was told to release layer 2 once, it will continue
to release layer 2 on every shutdown of OpenBSC.
diff --git a/src/input/misdn.c b/src/input/misdn.c
index 77da77c..de8d41f 100644
--- a/src/input/misdn.c
+++ b/src/input/misdn.c
@@ -445,9 +445,8 @@
 			return -EIO;
 		}
 
-		if (e1i_ts->type == E1INP_TS_TYPE_SIGN && release_l2) {
-			int clean = 1;
-			ret = ioctl(bfd->fd, IMCLEAR_L2, &clean);
+		if (e1i_ts->type == E1INP_TS_TYPE_SIGN) {
+			ret = ioctl(bfd->fd, IMCLEAR_L2, &release_l2);
 			if (ret < 0) {
 				fprintf(stderr, "could not send IOCTL IMCLEAN_L2 %s\n", strerror(errno));
 				return -EIO;