Connectivity metrics: add WakeupStats events

This patch defines a new WakeupStats event in ipconnectivity.proto and
populates these events from the NFLOG wakeup events stored in
NetdEventListenerService.

There is one WakeupStats object per known interface on which ingress
packets arrive and may wake the system up.

Example from $ adb shell dumpsys connmetrics list:

UPDATEME
...
WakeupStats(wlan0, total: 58, root: 0, system: 3, apps: 38, non-apps: 0, unrouted: 17, 6111s)
WakeupEvent(13:36:31.686, iface wlan0, uid -1)
WakeupEvent(13:38:50.846, iface wlan0, uid -1)
WakeupEvent(13:39:16.676, iface wlan0, uid 10065)
WakeupEvent(13:40:32.144, iface wlan0, uid 1000)
WakeupEvent(13:40:35.827, iface wlan0, uid 1000)
WakeupEvent(13:40:47.913, iface wlan0, uid 10004)
WakeupEvent(13:40:52.622, iface wlan0, uid 10014)
WakeupEvent(13:41:06.036, iface wlan0, uid 10004)
...

Bug: 34901696
Bug: 62179647
Test: runtest frameworks-net
Change-Id: Ie2676b20bfb411a1902f4942643df0c20e268d99