Added more descriptive data disallowed reasons

Splitted the vague APN_NOT_CONNECTABLE reason
with 3 more descriptive reasons DATA_IS_CONNECTING
, DATA_IS_DISCONNECTING, and DATA_ALREADY_CONNECTED

Test: Manual
Bug: 162007001
Merged-In: Ida1ea8d50c31b9c3b45e597aa52b366a17c487a6
Change-Id: Ida1ea8d50c31b9c3b45e597aa52b366a17c487a6
(cherry picked from commit 2a3ebb54)