osmux: Allow to enforce using Osmux for the client

Some systems only want to use Osmux. In case only Osmux
should be used fail if it has not be offered/acked.

Client:

Verified On, Off and Only with X-Osmux: 3 and without this field.
<000b> mgcp_protocol.c:823 Osmux only and no osmux offered on 0x14
<000b> mgcp_protocol.c:884 Resource error on 0x14

NAT:

Not tested and implemented

Fixes: OW#1492
3 files changed
tree: a07e1129f0d0fc5f711dc256f0c9e45afac49306
  1. debian/
  2. hlrsync/
  3. linux-kernel/
  4. openbsc/
  5. wireshark/
  6. .gitignore