net: phy: add a new phy_device flag to keep preamble before sfd

net: phy: add a new phy_device flag to keep preamble before sfd

Add a new flag, PHY_F_KEEP_PREAMBLE_BEFORE_SFD, to indicate that the PHY
shall not remove the preamble before the SFD if it supports it. MACs
that do not support receiving frames without a preamble can set this
flag.

Signed-off-by: Stefan Eichenberger <stefan.eichenberger@toradex.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Tested-by: Maxime Chevallier <maxime.chevallier@bootlin.com>
Reviewed-by: Maxime Chevallier <maxime.chevallier@bootlin.com>
Link: https://patch.msgid.link/20260120203905.23805-2-eichest@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>