Always call processResponseDone() NATT Responses

In case of errors, stopkeepaliveReponse wasn't calling
processResponseDone(), which leads to a wakelock being
held incorrectly. Move the processResponseDone() to
finally blocks to ensure that it's always called for
any non-null response message.

Bug: 116766779
Test: compilation
Change-Id: I0ced3fa19804f2fa422aaebd039dcaac40156dd9