Perform NTP lookup at Mobile data connections

If NITZ isn't supported by the current carrier the Android framework
relies instead on a remote NTP server to set the system clock. The
NetworkTimeUpdateService class polls for NTP time during the first 4
minutes after boot, failing to get NTP time within these minutes will
increase the polling interval to 24 hours. Hence, if a data connection
isn't activated directly after boot it can take a long time for the
system clock to be updated. To prevent this situation, NTP lookup is
scheduled as soon as a Mobile data connection has been established.

Change-Id: I046e0330147e7ace4b720a7e70f9d5047d42cfe6