For Akaros-mode, return symlink value in stat

We coopt Muid, since nobody but Plan 9 ever implemented it
anyway.

I realize we should have 9p2000.sane or something but
the way that dotu was implemented in here is going to require
so much change that I'm going with this hack for now.

Signed-off-by: Ronald G. Minnich <rminnich@google.com>