Documentation: networking: Fix missing PSE documentation and grammar issues

Documentation: networking: Fix missing PSE documentation and grammar issues

Fix a missing end of phrase in the documentation. It describes the
ETHTOOL_A_C33_PSE_ACTUAL_PW attribute, which was not fully explained.

Also, fix grammar issues by using simple present tense instead of
present continuous.

Reviewed-by: Oleksij Rempel <o.rempel@pengutronix.de>
Signed-off-by: Kory Maincent <kory.maincent@bootlin.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/20240912090550.743174-1-kory.maincent@bootlin.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>