net: usb: smsc95xx: add support for ethtool pause parameters

net: usb: smsc95xx: add support for ethtool pause parameters

Implement ethtool .get_pauseparam and .set_pauseparam handlers for
configuring flow control on smsc95xx. The driver now supports enabling
or disabling transmit and receive pause frames, with or without
autonegotiation. Pause settings are applied during link-up based on
current PHY state and user configuration.

Previously, the driver used phy_get_pause() during link-up handling,
but lacked initialization and an ethtool interface to configure pause
modes. As a result, flow control support was effectively non-functional.

Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Link: https://patch.msgid.link/20250718075157.297923-1-o.rempel@pengutronix.de
Signed-off-by: Jakub Kicinski <kuba@kernel.org>