Pack headroom into ctx - this way when we get a buffer we can figure out
the actual headroom that was allocated for the buffer. Will be helpful
to optimize switching between XDP and non-XDP modes which have different
headroom requirements.
Signed-off-by: NJason Wang <jasowang@redhat.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>