hv_netvsc: Pass net_device parameter to revoke and teardown functions

The callers to netvsc_revoke_*_buf() and netvsc_teardown_*_gpadl()
already have their net_device instances. Pass them as a paramaeter to
the function instead of obtaining them from netvsc_device struct
everytime

Signed-off-by: Mohammed Gamal <mgamal@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>