uml: make mconsole_stack namespace-aware

Also fixed the include syntax while I was there.

Signed-off-by: Jeff Dike <jdike@linux.intel.com>
Cc: Pavel Emelyanov <xemul@openvz.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>