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>
diff --git a/src/mm-broadband-modem.c b/src/mm-broadband-modem.c
index 702ddc5..5d3ac8a 100644
--- a/src/mm-broadband-modem.c
+++ b/src/mm-broadband-modem.c
@@ -3813,7 +3813,7 @@
                                              callback,
                                              user_data,
                                              unsolicited_registration_events_context_new);
-    ctx->enable = FALSE;
+    ctx->enable = enable;
     ctx->run_cs = cs_supported;
     ctx->run_ps = ps_supported;
     ctx->run_eps = eps_supported;