We need to compute the frame virtual address at different points.
Do it once.

Following patch will use the new va address for validate_loopback()
Signed-off-by: NEric Dumazet <edumazet@google.com>
Acked-by: NTariq Toukan <tariqt@mellanox.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>