net/mlx5e: RX, Dedicate a function for copying SKB header

Get the logic of copying the packet header into the SKB linear part
into a generic function. Function does copy length alignment
and dma buffer sync.

It is currently called only within the MPWQE flow.
In a downstream patch, it will be called within the legacy RQ flow
as well.

Signed-off-by: Tariq Toukan <tariqt@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>