r8169: skip DASH fw status checks when DASH is disabled

On devices that support DASH, the current code in the "rtl_loop_wait" function
raises false alarms when DASH is disabled. This occurs because the function
attempts to wait for the DASH firmware to be ready, even though it's not
relevant in this case.

r8169 0000:0c:00.0 eth0: RTL8168ep/8111ep, 38:7c:76:49:08:d9, XID 502, IRQ 86
r8169 0000:0c:00.0 eth0: jumbo features [frames: 9194 bytes, tx checksumming: ko]
r8169 0000:0c:00.0 eth0: DASH disabled
...
r8169 0000:0c:00.0 eth0: rtl_ep_ocp_read_cond == 0 (loop: 30, delay: 10000).

This patch modifies the driver start/stop functions to skip checking the DASH
firmware status when DASH is explicitly disabled. This prevents unnecessary
delays and false alarms.

The patch has been tested on several ThinkStation P8/PX workstations.

Fixes: 0ab0c45d

 ("r8169: add handling DASH when DASH is disabled")
Signed-off-by: Atlas Yu <atlas.yu@canonical.com>
Reviewed-by: Heiner Kallweit <hkallweit1@gmail.com>
Link: https://lore.kernel.org/r/20240328055152.18443-1-atlas.yu@canonical.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>