telephony: PreferredAPN is not set correctly while device is booting

When device is booting, mPhone.getSubId() return -2.
It makes device get the wrong preferredAPN.

Bug: 23367895
Change-Id: Ieadab013521e81d224ff08e4a60c2d9222cd6578
Signed-off-by: wooje.shim <wooje.shim@lge.com>
Signed-off-by: Sungmin Choi <sungmin.choi@lge.com>