Properly null-terminate ifreq::irf_name

It's unclear whether it has to be, but there are a lot of patches floating around
on the net that indicate that Coverty requires this, and the SIOCGIFADDR micro-howto
also NUL-terminates the string.

So who is Qt to differ?

Change-Id: I1aa5a2de47a58b1d9b73556d5a6ddc48b2c40ce3
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/plugins/bearer/generic/qgenericengine.cpp

@@ -165,6 +165,7 @@ static QNetworkConfiguration::BearerType qGetInterfaceType(const QString &interf
 
     ifreq request;
     strncpy(request.ifr_name, interface.toLocal8Bit().data(), sizeof(request.ifr_name));
+    request.ifr_name[sizeof(request.ifr_name) - 1] = '\0';
     int result = ioctl(sock, SIOCGIFHWADDR, &request);
     close(sock);