Handle invalid arguments case correctly

:Release Notes:
Fix issue with incorrect luna responses sent for "setstate" API by correct
handling of "invalid arguments" error case.

:Detailed Notes:
The "setstate" API in com.palm.wifi interface was sending an "invalid arguments"
error along with the "success" message, because of a missing goto statement.
This has been fixed with this change.

:Testing performed:
The fix has been tested by calling "setstate" API multiple times, alternately
enabling and disabling wifi, but every time only a success message was
seen, the "invalid arguments" error was never seen.

:Issues Addressed:
[GF-8070] com.palm.wifi service behaves strange

Open-webOS-DCO-1.0-Signed-off-by: Sapna Todwal <sapna.todwal@lge.com>

Change-Id: Idf13f0edf379dc80905b9e3231ffe683891d485f
Reviewed-on: https://g2g.palm.com/2911
Reviewed-by: Sapna Todwal <sapna.todwal@lge.com>
Tested-by: Sapna Todwal <sapna.todwal@lge.com>