feat(net): add VIRTIO_NET_F_MRG_RXBUF support to virtio-net device

Implement VIRTIO_NET_F_MRG_RXBUF feature for VirtIO network device.
It allows receiving a single network frame into multiple descriptor
chains. The amount of descriptor chains (also known as heads) that were
used is written into the `virtio_net_hdr_v1` structure which is located
at the beginning of the guest buffer.

Signed-off-by: Egor Lazarchuk <[email protected]>

Author: ShadowCurse