x86_64: csum_add for x86_64

Add csum_add function for x86_64.
Signed-off-by: Tom Herbert <therbert@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

arch/x86/include/asm/checksum_64.h

@@ -188,4 +188,11 @@ static inline unsigned add32_with_carry(unsigned a, unsigned b)
 	return a;
 }
 
+#define HAVE_ARCH_CSUM_ADD
+static inline __wsum csum_add(__wsum csum, __wsum addend)
+{
+	return (__force __wsum)add32_with_carry((__force unsigned)csum,
+						(__force unsigned)addend);
+}
+
 #endif /* _ASM_X86_CHECKSUM_64_H */