Ensure that struct sockaddr is long enough...

src/include/gpxe/socket.h

 /** A socket address family */
 typedef uint16_t sa_family_t;
 
+/** Length of a @c struct @c sockaddr */
+#define SA_LEN 32
+
 /**
  * Generalized socket address structure
  *
 	 * This is an AF_XXX constant.
 	 */
         sa_family_t sa_family;
+	/** Padding
+	 *
+	 * This ensures that a struct @c sockaddr_tcpip is large
+	 * enough to hold a socket address for any TCP/IP address
+	 * family.
+	 */
+	char pad[ SA_LEN - sizeof ( sa_family_t ) ];
 };
 
 #endif /* _GPXE_SOCKET_H */

src/include/gpxe/tcpip.h

  */
 #define TCPIP_EMPTY_CSUM 0xffff
 
-/** Length of a @c struct @c sockaddr_tcpip */
-#define SA_TCPIP_LEN 32
-
 /**
  * TCP/IP socket address
  *
 	 * enough to hold a socket address for any TCP/IP address
 	 * family.
 	 */
-	char pad[SA_TCPIP_LEN - sizeof ( sa_family_t ) - sizeof ( uint16_t )];
+	char pad[ sizeof ( struct sockaddr ) -
+		  ( sizeof ( sa_family_t ) + sizeof ( uint16_t ) ) ];
 };
 
 /**