Fix for empty RSSI triangle after boot

After device bootup, the signal strength triangle is empty although there is
both voice and data connection. This is due to when TelephonyRegistry doing call
back listen register, some APP use mDefaultSubID. However, when the reigister
happen, the mDefaultSubId does not exist. Althouhgh it can be update later, if
the update event comes too late (especially after the steady state), no
ServiceStatechange event can be received anymore. Thus the service is always not
available and the signal stength trangle has no chance to be updated anymore.
This is a risk condition.

Bug:17472622

Change-Id: I8e6e37469086eecabbc4b9abcdb0d32eb09e0635