Fix: Use snprintf() for device path generation

Compilation warning:

mibgroup/ucd-snmp/diskio_linux.c: In function 'diskio_parse_config_disks':
mibgroup/ucd-snmp/diskio_linux.c:184:5: warning: '__builtin___strncat_chk' output may be truncated copying 1023 bytes from a string of length 1023 [-Wstringop-truncation]
  184 |     strncat(device, path, STRMAX - 1);
      |     ^

Use of strncat() is totally insecure for any buffer overruns attacks (see 'man strncat' for details).
Fix it with use more friendly function to string end '\0'.

Author: KuzinAndrey

agent/mibgroup/ucd-snmp/diskio_linux.c

@@ -177,11 +177,8 @@ add_device(char *path, int addNewDisks)
     }
 
     /* first find the path for this device */
-    device[0] = '\0';
-    if (*path != '/') {
-        strlcpy(device, "/dev/", STRMAX - 1);
-    }
-    strncat(device, path, STRMAX - 1);
+    if (STRMAX <= snprintf(device, STRMAX, "%s%s", (*path != '/') ? "/dev/" : "", path))
+        netsnmp_config_error("Device path '%s' is too long and was truncated to '%s'", path, device);
 
     /* check for /dev existence */
     if (stat(device, &stbuf) != 0) {    /* ENOENT */