When setting up connectivity, e.g. with new network detection, the pref
wouldn't be checked (or honored), resulting in spurious startup calls
despite being preffed off. This fixes that.
Resolves#1474
Log spam fix. Suppresses 1,100 instances of NS_ENSURE_SUCCESS(rv, rv) failed with result 0x80520012 emitted from netwerk/base/nsIOService.cpp during linux64 debug testing. Backports [m-c 1333174](https://bugzilla.mozilla.org/show_bug.cgi?id=1333174).
