Improving the demuxer functions

[Justus Winter]

Hi :)

the way our demuxer functions chain the X_server functions is
initializing the reply message over and over again. This can be
avoided by following the recommendations of the Mach Server Writer's
Guide. A patch for libdiskfs is sent as a follow-up.

To improve the situation further, I propose to change mig so that the
X_server_routine functions can be inlined into the demuxer function to
avoid the function call overhead just to test whether the msgh_id is
in range.

Cheers,
Justus