QNativeWifiEnginePlugin: replace a volatile bool with an atomic int

QNativeWifiEnginePlugin: replace a volatile bool with an atomic int

Since there is non-atomic data that is protected by 'triedResolve',
the (outer) read from triedResolve needs to have acquire, and the
store needs to have release semantics. The release implied by the
mutex unlock is not good enough because it only synchronises-with
the locking of the same mutex, which not all threads execute.

Change-Id: I90b62c4c0213472ecf2b95a1674a1c6c79dc3786
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Reviewed-by: Shane Kearns <shane.kearns@accenture.com>