cherrypick from mnc-dev docs: Fix return info for checkSelfPermission()

Original change-Id: 4276a8fb

Docs incorrectly said the method returns a boolean. In fact,
it (like the framework version) returns an int constant.

See first comment for doc stage location.

bug: 23331110
Change-Id: I2b4ccdc56dc0cff414c4d21e3916e8e7a0b0e909
(cherry picked from commit 4276a8fb)