Fix bridge routines detection on kFreeBSD

In order to properly detect bridge related definitions such as
BRDGSFD, BRDGADD and BRDGDEL on kFreeBSD we need to include
<stdint.h>.

http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=715321

Reported by Laurent Bigonville.

configure.ac

@@ -2405,7 +2405,8 @@ AC_CHECK_DECLS([BRDGSFD, BRDGADD, BRDGDEL],
                           [1],
                           [whether BSD style bridge management is available])],
                [],
-               [#include <net/if.h>
+               [#include <stdint.h>
+                #include <net/if.h>
                 #include <net/ethernet.h>
                 #include <net/if_bridgevar.h>
                ])