Use a union to let struct sockaddr have the same alignment requirements as struct sockaddr_in

src/include/lwip/sockets.h

@@ -59,7 +59,13 @@ struct sockaddr_in {
 struct sockaddr {
   u8_t sa_len;
   u8_t sa_family;
-  char sa_data[14];
+  union {
+    char bytes[14];
+    struct {
+      u16_t a1;
+      u32_t a2;
+    } alignment;
+  } sa_data;
 };
 
 #ifndef socklen_t