Only define sa_family_t once.

Change-Id: Icf700910c836d22c8a27ad026ec8af11697edd5a
diff --git a/libc/include/sys/socket.h b/libc/include/sys/socket.h
index 85999f3..9736ba8 100644
--- a/libc/include/sys/socket.h
+++ b/libc/include/sys/socket.h
@@ -40,10 +40,11 @@
 #include <linux/types.h>
 #include <linux/compiler.h>
 
+#include <bits/sa_family_t.h>
+
 __BEGIN_DECLS
 
 #define sockaddr_storage __kernel_sockaddr_storage
-typedef unsigned short sa_family_t;
 
 struct timespec;