Fix Windows build

Change-Id: I66ecb9f89ec13e432e888e3825d01a015b117568
Reviewed-on: https://boringssl-review.googlesource.com/7505
Reviewed-by: David Benjamin <davidben@google.com>

crypto/bio/internal.h

@@ -67,6 +67,9 @@ typedef unsigned short u_short;
 #include <sys/types.h>
 #include <sys/socket.h>
 #else
+#pragma warning(push, 3)
+#include <winsock2.h>
+#pragma warning(pop)
 typedef int socklen_t;
 #endif