hw/net/xilinx_ethlite: Introduce txbuf_ptr() helper

For a particular physical address within the EthLite MMIO range,
addr_to_port_index() returns which port is accessed.

txbuf_ptr() points to the beginning of a (RAM) TX buffer
within the device state.

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Edgar E. Iglesias <edgar.iglesias@amd.com>
Message-Id: <20241112181044.92193-10-philmd@linaro.org>
1 file changed