Update the SMS sending limit instantly (1/2)

Patch Set 2: observe the setting value instead of checking its value
every time

Patch Set 3: readd accidentally removed final modifier

Patch Set 4: remove redundant inner context variable

Change-Id: If8a0867945cf308391009eae168bf05a6dd429eb
Merge "Update the SMS sending limit instantly (1/2)" into cm-10.1