hw/net/can/xlnx-versal-canfd: Fix CAN FD flag check

hw/net/can/xlnx-versal-canfd: Fix CAN FD flag check

When checking the QEMU_CAN_FRMF_TYPE_FD flag, we need to ignore other
potentially set flags. Before this change, received CAN FD frames from
SocketCAN weren't being recognized as CAN FD.

Signed-off-by: Doug Brown <doug@schmorgal.com>
Reviewed-by: Pavel Pisa <pisa@cmp.felk.cvut.cz>
Reviewed-by: Francisco Iglesias <francisco.iglesias@amd.com>
Message-id: 20240827034927.66659-3-doug@schmorgal.com
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>