[socket] Ensure socket address structure sizes are fixed

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/include/ipxe/fc.h

 	 */
 	char pad[ sizeof ( struct sockaddr ) - sizeof ( sa_family_t )
 					     - sizeof ( struct fc_port_id ) ];
-} __attribute__ (( may_alias ));
+} __attribute__ (( packed, may_alias ));
 
 extern struct fc_port_id fc_empty_port_id;
 extern struct fc_port_id fc_f_port_id;

src/include/ipxe/in.h

 		    sizeof ( uint16_t ) /* sin_flags */ +
 		    sizeof ( uint16_t ) /* sin_port */ +
 		    sizeof ( struct in_addr ) /* sin_addr */ ) ];
-} __attribute__ (( may_alias ));
+} __attribute__ (( packed, may_alias ));
 
 /**
  * IPv6 socket address
 		    sizeof ( uint16_t ) /* sin6_port */ +
 		    sizeof ( uint16_t ) /* sin6_scope_id */ +
 		    sizeof ( struct in6_addr ) /* sin6_addr */ ) ];
-} __attribute__ (( may_alias ));
+} __attribute__ (( packed, may_alias ));
 
 extern int inet_aton ( const char *cp, struct in_addr *inp );
 extern char * inet_ntoa ( struct in_addr in );

src/include/ipxe/socket.h

 	 * family.
 	 */
 	char pad[ SA_LEN - sizeof ( sa_family_t ) ];
-} __attribute__ (( may_alias ));
+} __attribute__ (( packed, may_alias ));
 
 /**
  * Socket address converter

src/include/ipxe/tcpip.h

 		  ( sizeof ( sa_family_t ) /* st_family */ +
 		    sizeof ( uint16_t ) /* st_flags */ +
 		    sizeof ( uint16_t ) /* st_port */ ) ];
-} __attribute__ (( may_alias ));
+} __attribute__ (( packed, may_alias ));
 
 /** 
  * A transport-layer protocol of the TCP/IP stack (eg. UDP, TCP, etc)