Staging: wlan-ng: Cleanup wlan_compat.h more

Move version identifier into p80211netdev.h and rename it to 0.3.0-staging
to differentiate from the out-of-tree version.

Also remove the unused wlan_ethconv declaration.

Signed-off-by: Moritz Muehlenhoff <jmm@debian.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>