Revert "virtio/vsock: fix header length on skb merging"

This reverts commit 830c11c9 which is
commit f7154d96 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: I5d7ea0bc99094712815a8f1a13a0db4278e7e980
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>