net: stmmac: selftests: Don't test flow control for small rx fifos

net: stmmac: selftests: Don't test flow control for small rx fifos

On dwmac1000, dwmac4 and dwxgmac, we only emit pause frames if there's
at least 4096 bytes in each queue's fifo.

The phylink mac capabilities are still MAC_ASYM_PAUSE | MAC_SYM_PAUSE as
otherwise we won't be able to negotiate 'rx on' pause. ASYM only will
prevent negotiating 'rx off tx on', while SYM only doesn't really
matche the reality (not symmetric if we can only do RX pause).

Fixes: 091810dbded9 ("net: stmmac: Introduce selftests support")
Signed-off-by: Maxime Chevallier <maxime.chevallier@bootlin.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Link: https://patch.msgid.link/20260826140500.616466-7-maxime.chevallier@bootlin.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>