Changes

Bump version: 0.3.0 → 0.4.0

Release highlights:

* SYS#7065: fixed statsd reports format
* SYS#7066: REST (M2M/VTY) interface, osmo-s1gw-cli
* SYS#7307: GTP-U KPI metrics (using nftables)
* SYS#7309: S1 HANDOVER procedure support
* SYS#7332: migrated from escript to releases
* SYS#7594: eNB uptime statistics
* SYS#7734: proper PFCP Network Instance IE encoding
* GSMTAP logging handler

Change-Id: I002bc911e3a98be7c562895b0bd4a82f03648971