Fix possible buffer size problem (CWE-120)

Calling strncpy with a maximum size argument of 16 bytes on
destination array "iwr.ifr_ifrn.ifrn_name" of size 16 bytes
might leave the destination string unterminated.

Author: frenzymadness

python-ethtool/ethtool.c

@@ -666,7 +666,8 @@ static PyObject *get_wireless_protocol (PyObject *self __unused, PyObject *args)
 
     /* Setup our request structure. */
     memset(&iwr, 0, sizeof(iwr));
-    strncpy(iwr.ifr_name, devname, IFNAMSIZ);
+    strncpy(iwr.ifr_name, devname, IFNAMSIZ-1);
+    iwr.ifr_name[IFNAMSIZ-1] = 0;
 
     /* Open control socket. */
     fd = socket(AF_INET, SOCK_DGRAM, 0);