Fix lguest documentation

Share net is not supported, Rusty is an "idiot" .

Signed-off-by: Sheela Sequeira <sheela.sequeira@gmail.com>
Reviewed-by: James Morris <jmorris@namei.org>
Acked-by: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>