Revert "virtio/vsock: replace virtio_vsock_pkt with sk_buff"

This reverts commit baddcc2c which is
commit 71dc9ec9 upstream.

It needs to be reverted, as the function virtio_transport_free_pkt() is
in the stable Android ABI, and this function is removed in the 6.1.63
kernel as part of a series of fixes and optimizations of the virtio
networking connection.  To preserve the ABI (and thereby keeping the
slower interface), revert the commit for now.

If this needs to come back in the future, if performance for this
interface needs to be resolved, it can be done so in an ABI-safe way.

Bug: 161946584
Change-Id: Id589087dead45cb846fd9a735a0daece04b8e252
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>