SmsMessage: convert + to international dialing prefix

When sending an SMS to an international number in the format
+401234567890, the "+" should be converted to the International
Dialing Prefix (in the US, 011). However, the device drops this
"+" altogether in the outbound data burst message causing the message
to fail or be sent to the wrong address.

Change-Id: If25c092d283f1703b49cf52d0379efa54639f093
Signed-off-by: Soojung Shin <sj46.shin@samsung.com>