staging: fsl-dpaa2/eth: Fix access to FAS field

Commit 4b2d9fe8 ("staging: fsl-dpaa2/eth: Extra headroom in RX
buffers") removes the software annotation (SWA) area from the RX
buffer layout, as it's not used by anyone, but fails to update the
macros for accessing hardware annotation (HWA) fields, which is
right after the SWA in the buffer headroom.

This may lead to some frame annotation status fields (e.g. indication
if L3/L4 checksum is valid) to be read incorrectly.

Turn the accessor macros into inline functions and add a bool param
to specify if SWA is present or not.

Fixes: 4b2d9fe8

 ("staging: fsl-dpaa2/eth: Extra headroom in RX buffers")

Signed-off-by: Ioana Radulescu <ruxandra.radulescu@nxp.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>