Revert "virtio/vsock: don't use skbuff state to account credit"

This reverts commit 5852a2b5 which is
commit 07770616 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: I6607855de7742319460554c4b81edbce0aab0c37
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>