Avoid unaligned fetch in ladr_match()

Avoid unaligned fetch in ladr_match()

There is no guarantee that the PCNetState is allocated such that
csr[8] is allocated on an 8-byte boundary.  Since not all hosts are
capable of unaligned fetches the 16-bit elements need to be fetched
individually to avoid a potential fault.  Closes issue #2143

Resolves: https://gitlab.com/qemu-project/qemu/-/issues/2143
Signed-off-by: Nick Briggs <nicholas.h.briggs@gmail.com>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Jason Wang <jasowang@redhat.com>