ip: crash in ip_csum_fold due to illegal instruction shrx
Encounter a crash for the line
shrx   edi,eax,edi
in ip_csum_fold. The target cpu is ivy bridge which does not support
shrx instruction.
Type: fix
Fixes:
@@ -301,7 +301,7 @@ always_inline u16
ip_csum_fold (ip_csum_t c)
{
/* Reduce to 16 bits. */
-#ifdef __x86_64__
+#if defined(__x86_64__) && defined(__BMI2__)
u64 tmp;
asm volatile(
/* using ADC is much faster than mov, shift, add sequence
