vts(wifi): Stop wifi fully instead of stopping framework

Stopping entire framework can cause other essential services to be
stopped. When wifi is stopped, it does not interact with any of the
wifi HAL's.

Bug: 168278011
Test: atest --iterations 10
VtsHalWifiSupplicantP2pV1_0TargetTest
VtsHalWifiSupplicantP2pV1_1TargetTest
VtsHalWifiSupplicantP2pV1_2TargetTest
VtsHalWifiSupplicantP2pV1_3TargetTest
Change-Id: Ia93e78cf4c147e42dd3d68e24a582c0c1af15899