ipaccess: memset the tlv_parsed structure before parsing

Make sure the tlv_parsed structure is initialized properly,
otherwise we might detect a tag that should not be present.
diff --git a/openbsc/src/input/ipaccess.c b/openbsc/src/input/ipaccess.c
index 4968e80..74c850c 100644
--- a/openbsc/src/input/ipaccess.c
+++ b/openbsc/src/input/ipaccess.c
@@ -101,6 +101,8 @@
 	u_int8_t t_tag;
 	u_int8_t *cur = buf;
 
+	memset(dec, 0, sizeof(*dec));
+
 	while (cur < buf + len) {
 		t_len = *cur++;
 		t_tag = *cur++;