Merge branch 'zecke/fixes/osmux-nat'

The osmux code doesn't work if the MGCP MGW is behind a NAT (which
is likely to be the case). The usage of endp->ci is troublesome too
not only because of the uint8_t vs. uint32_t mismatch but because
this identity is generated by the MGCP MGW and can clash. This means
that with two clients the wrong call might be connected.

The next bigger thing is that old handles are never cleared. This
code is clearly not ready for deployment.