net: sfp: add quirk for OEM 2.5G optical modules

net: sfp: add quirk for OEM 2.5G optical modules

Some OEM-branded SFP modules are incorrectly detected as
1000Base-X and fail to establish link on 2.5G-capable ports.

These modules do not properly advertise 2500Base-X capability
in their EEPROM and require forcing the correct SerDes mode.

Add sfp_quirk_2500basex for:

  - OEM SFP-2.5G-LH03-B
  - OEM SFP-2.5G-LH20-A

Both modules report:

  Vendor name: OEM
  Vendor PN: SFP-2.5G-LH03-B / SFP-2.5G-LH20-A

Tested on OpenWrt with successful 2.5G link establishment.

Signed-off-by: Wei Qisen <weixiansen574@163.com>
Link: https://patch.msgid.link/20260526055206.1750-1-weixiansen574@163.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>