hv_netvsc: Split netvsc_revoke_buf() and netvsc_teardown_gpadl()

Split each of the functions into two for each of send/recv buffers.
This will be needed in order to implement a fine-grained messaging
sequence to the host so that we accommodate the requirements of
different Windows versions

Fixes: 0ef58b0a

 ("hv_netvsc: change GPAD teardown order on older versions")
Signed-off-by: Mohammed Gamal <mgamal@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>