Fix the variable for the packet length.

The length passed in is a u_int, so we should assign it to a u_int, not
a u_short.
diff --git a/print-isoclns.c b/print-isoclns.c
index 5a0b428..eef8d6e 100644
--- a/print-isoclns.c
+++ b/print-isoclns.c
@@ -2279,7 +2279,8 @@
     uint8_t ext_is_len, ext_ip_len, mt_len;
     uint8_t isis_subtlv_idrp;
     const uint8_t *optr, *pptr, *tptr;
-    u_short packet_len,pdu_len, key_id;
+    u_int packet_len;
+    u_short pdu_len, key_id;
     u_int i,vendor_id;
     int sigcheck;