net: airoha: Make flow control source port mapping dependent on nbq parameter

net: airoha: Make flow control source port mapping dependent on nbq parameter

Flow control source port mapping for USB serdes needs to be configured
according to the GDM port nbq parameter. This is a preliminary patch
since nbq parameter is specific for the given port serdes and needs to
be read from the DTS (in the current codebase is assigned statically).

Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Link: https://patch.msgid.link/20260306-airoha-fix-loopback-for-usb-serdes-v2-1-319de9c96826@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>