[PATCH] Clarify help text of SKGE/SK98LIN/SKY2

Some users have commented that it is unclear which driver they should be
using for their Marvell/SysKonnect network adapter, and which ones
are/aren't interchangable.

This patch attempts to reduce the confusion.

Signed-off-by: Daniel Drake <dsd@gentoo.org>
Signed-off-by: Jeff Garzik <jgarzik@pobox.com>