NetworkMonitor: improve captive portal validation logs

This patch adds probe type and url to all validation logs about web
probes sent for captive portal detection.

Test: built, flashed, looked at $ adb shell dumpsys connectivity
Bug: 36830206, 36532213
Merged-In: Iee2caaf6664f3d097f9d1888ccc5fece0a95994c

(cherry picked from commit d9ac87ed)

Change-Id: I5ab8bb117d2bbad123136dfbbf78cbe84a7f688e