Add unitest and change invalid function name.

Add unitest and change invalid function name.

1. Add unittest for NSProviderRegisterTopic case.
2. change invalid function name in NSProviderInterface.h

second patch is comment changed only.

third patch included,
change invalid testcase name.

Change-Id: Iacbc8466c1f2f204b81ff5db28015ef9f5762858
Signed-off-by: jaesick.shin <jaesick.shin@samsung.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/11195
Tested-by: jenkins-iotivity <jenkins-iotivity@opendaylight.org>
Reviewed-by: Uze Choi <uzchoi@samsung.com>