vt: fix background color on line feed, DEC invert

Original report: """I used to force my console to black-on-white by the
command `setterm -inversescreen on`.  In 2.6.26-rc4, I get lots of black
background characters."""

Another addendum to commit c9e587ab.  This was previously missed out since
I was not aware of what vc_decscnm was for.

Signed-off-by: Jan Engelhardt <jengelh@medozas.de>
Reported-by: <thunder7@xs4all.nl>
Tested-by: <thunder7@xs4all.nl>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>