rfkill: Always sync state on construction

This fixes an issue where the indicator can be out of sync until the
RfkillManager (used by it) properties change.

The problem is that multiple instances of the indicator will use
the same RfkillManager instance (getRfkillManager() returns a singleton)
that only guarantees to emit the changed signal in two scenarios:
when the D-Bus proxy connects and when the proxy properties change.

If by the time an indicator is instantiated the RfkillManager's D-Bus
proxy is already connected, that indicator would only sync its state
when the RfkillManager properties change.

Let's fix that by always syncing the state on construction - in the worst
case scenario the RfkillManager's D-Bus proxy won't have connected yet
and the indicator state will be temporarily out of sync but once it gets
connected the indicator will sync again with the correct state.

GNOME/gnome-shell!1386
9 jobs for !1386 with rfkill-indicator-always-sync in 4 minutes and 3 seconds (queued for 2 seconds)
detached
Status Job ID Name Coverage
  Review
passed #835863
check_commit_log

00:00:27

passed #835865
eslint

00:01:06

passed #835864
js_check

00:00:32

passed #835867
no_template_check

00:00:31

passed #835866
potfile_check

00:00:25

 
  Build
passed #835868
build

00:02:09

passed #835869
flatpak
flatpak

00:01:24

 
  Test
passed #835870
test

00:00:45

passed #835871
test-pot

00:00:46