Fix network performance issue on arm64 for runv
Fix network performance issue on arm64 for runv

Network performance in runv is lower significantly
than in virtual machine started by qemu,as vnet_hdr
feature is not enabled in runv when get access to
a tun/tap device. Adding CIFF_VNET_HDR flag to GetTapFd
func will fixed that issue.

Signed-off-by: Jianyong Wu <014b326f98f2666b9e003df03885e42c010251d5@arm.com>
Signed-off-by: Wei Chen <7bda119aa2bd1d28c0fb067e862b11d5acc5fc93@arm.com>

laijs/runv,hyperhq/runv,hyperhq/runv,hyperhq/runv,laijs/runv,laijs/runv