Include headers when using ovs_rundir

This patch adds an additional include file while compiling under MSVC.

Found by compiling under MSVC x64 and hitting the following problem:
http://stackoverflow.com/questions/23144151/64-bit-function-returns-32-bit-pointer

Signed-off-by: Alin Gabriel Serdean <aserdean@cloudbasesolutions.com>
Signed-off-by: Gurucharan Shetty <gshetty@nicira.com>

lib/stream-tcp.c

@@ -76,6 +76,8 @@ const struct stream_class tcp_stream_class = {
 };
 
 #ifdef _WIN32
+#include "dirs.h"
+
 static int
 windows_open(const char *name, char *suffix, struct stream **streamp,
              uint8_t dscp)