[tcpip] Do not fall back to using unoptimised TCP/IP checksumming

Require architecture-specific code to make a deliberate choice to use
the unoptimised generic_tcpip_continue_chksum() function, if there is
no optimised version available.

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

src/arch/x86/core/x86_tcpip.c

  * @v len		Length of data buffer
  * @ret cksum		Updated checksum, in network byte order
  */
-uint16_t x86_tcpip_continue_chksum ( uint16_t partial,
-				     const void *data, size_t len ) {
+uint16_t tcpip_continue_chksum ( uint16_t partial, const void *data,
+				 size_t len ) {
 	unsigned long sum = ( ( ~partial ) & 0xffff );
 	unsigned long initial_word_count;
 	unsigned long loop_count;

src/arch/x86/include/bits/tcpip.h

 
 FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
 
-extern uint16_t x86_tcpip_continue_chksum ( uint16_t partial,
-					    const void *data, size_t len );
-
-#define tcpip_continue_chksum x86_tcpip_continue_chksum
+extern uint16_t tcpip_continue_chksum ( uint16_t partial, const void *data,
+					size_t len );
 
 #endif /* _BITS_TCPIP_H */

src/include/ipxe/tcpip.h

 #include <ipxe/socket.h>
 #include <ipxe/in.h>
 #include <ipxe/tables.h>
+
+extern uint16_t generic_tcpip_continue_chksum ( uint16_t partial,
+						const void *data, size_t len );
+
 #include <bits/tcpip.h>
 
 struct io_buffer;
 extern struct tcpip_net_protocol * tcpip_net_protocol ( sa_family_t sa_family );
 extern struct net_device * tcpip_netdev ( struct sockaddr_tcpip *st_dest );
 extern size_t tcpip_mtu ( struct sockaddr_tcpip *st_dest );
-extern uint16_t generic_tcpip_continue_chksum ( uint16_t partial,
-						const void *data, size_t len );
 extern uint16_t tcpip_chksum ( const void *data, size_t len );
 extern int tcpip_bind ( struct sockaddr_tcpip *st_local,
 			int ( * available ) ( int port ) );
 
-/* Use generic_tcpip_continue_chksum() if no architecture-specific
- * version is available
- */
-#ifndef tcpip_continue_chksum
-#define tcpip_continue_chksum generic_tcpip_continue_chksum
-#endif
-
 #endif /* _IPXE_TCPIP_H */