broadband-modem: fix enable flag in UnsolicitedRegistrationEventsContext

BUG=chromium-os:39528
TEST=Tested the following:
1. Verify that ModemManager uses AT+CREG=2 / AT+CGREG=2 / AT+CEREG=2 to
   enable unsolicited 3GPP registration update.
2. Verify that ModemManager uses AT+CREG=0 / AT+CGREG=0 / AT+CEREG=0 to
   disable unsolicited 3GPP registration update.

Change-Id: I6d3d5859bd4ce2691b0d8d455fffdcb4c908cc03
Reviewed-on: https://gerrit.chromium.org/gerrit/44666
Reviewed-by: Thieu Le <thieule@chromium.org>
Commit-Queue: Ben Chan <benchan@chromium.org>
Tested-by: Ben Chan <benchan@chromium.org>
1 file changed