sfc: SFX7101/SFT9001: Fix AN advertisements

All 10Xpress PHYs require autonegotiation all the time; enforce this
in the set_settings() method and do not treat it as a workaround.

Remove claimed support for 100M HD mode since it is not supported by
current firmware.

Do not set speed override bits when AN is enabled, and do not use
register 1.49192 for AN configuration as it can override what we set
elsewhere.

Always set the AN selector bits to 1 (802.3).

Fix confusion between Next Page and Extended Next Page.

Signed-off-by: Ben Hutchings <bhutchings@solarflare.com>
Signed-off-by: David S. Miller <davem@davemloft.net>