This commit modernizes the USB Gadget configuration to improve network
compatibility and handle USB-C Alt-Mode resource contention.
Key Changes:
1. RFC 3927 Compliance (Link-Local IP):
- Changed default IP from '10.1.1.2' to '169.254.170.2/16'.
- The previous 10.x address often conflicted with home subnets, causing
routing blackholes where LAN traffic was misrouted to the USB interface.
- Link-Local ensures zero conflict with routed networks and enables
automatic discovery on Windows/macOS/Linux hosts.
2. IPv6 Support:
- Added explicit 'fe80::2' link-local address assignment.
3. Smart Hotplug (USB-C/DP):
- Updated 'handle-hdmi-hotplug' regex to support DisplayPort (DP) events.
- Added logic to stop the 'usbgadget' service ONLY when a DisplayPort
connection is detected via sysfs. This prevents USB data lane contention
on SoCs where USB-C Video and USB Data share physical resources.
- Standard HDMI connections are unaffected.
Ref: #ROCKNIX-USB-001
