If the user has unchecked “Allow incoming connections” in
Settings->Options...->Network then fListen=false is saved in
~/.config/Bitcoin/Bitcoin-Qt.conf. This flips -listen to false
during startup, but leaves -listenonion to true.
This flipping of -listen is done in OptionsModel::Init() after
InitParameterInteraction() has been executed which would have flipped
-listenonion, should it have seen -listen being false
(this is a difference between bitcoind and bitcoin-qt).

