gbproxy support for "network sharing" via MOCN
In MOCN, the PS domain is also affected.
Likely required enhancements to osmo-gbproxy would include
- not only one pool of SGSNs, but multiple pools (one per CN)
- modifications to UL-UNITDATA/DL-UNITDATA processing related to redirect etc.
- logic for redirect handling based on redirection indication, redirect attempt flag, redirection completed