doc: release-notes-3.7: Add notes for selected network components

Added release notes for these network components:

* DNS/mDNS/LLMNR
* gPTP/PTP
* Sockets
* Capture API
* Virtual interface
* VLAN
* Wi-Fi

Signed-off-by: Jukka Rissanen <jukka.rissanen@nordicsemi.no>