udev: Fix build on older platforms

Caused by commit @d1eea6c1 due to the missing symbol on older platforms.

Signed-off-by: Erik Skultety <eskultet@redhat.com>

m4/virt-udev.m4

@@ -34,6 +34,14 @@ AC_DEFUN([LIBVIRT_CHECK_UDEV],[
      if test "$with_udev_logging" = "yes" ; then
         AC_DEFINE_UNQUOTED([HAVE_UDEV_LOGGING], 1, [whether libudev logging can be used])
      fi
+
+    old_CFLAGS="$CFLAGS"
+    old_LIBS="$LIBS"
+    CFLAGS="$CFLAGS $UDEV_CFLAGS"
+    LIBS="$CFLAGS $UDEV_LIBS"
+    AC_CHECK_FUNCS([udev_monitor_set_receive_buffer_size])
+    CFLAGS="$old_CFLAGS"
+    LIBS="$old_LIBS"
   fi
 ])
 

src/node_device/node_device_udev.c

@@ -1764,12 +1764,14 @@ static int nodeStateInitialize(bool privileged,
 
     udev_monitor_enable_receiving(priv->udev_monitor);
 
+#if HAVE_UDEV_MONITOR_SET_RECEIVE_BUFFER_SIZE
     /* mimic udevd's behaviour and override the systems rmem_max limit in case
      * there's a significant number of device 'add' events
      */
     if (geteuid() == 0)
         udev_monitor_set_receive_buffer_size(priv->udev_monitor,
                                              128 * 1024 * 1024);
+#endif
 
     /* We register the monitor with the event callback so we are
      * notified by udev of device changes before we enumerate existing