Revert "virtio/vsock: remove redundant 'skb_pull()' call"

This reverts commit 883a3db2 which is
commit 6825e6b4 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: I377797e7be1981ec41108b89c40d484197fd1082
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>