The command /usr/bin/ssh -o ControlPath=%C 0.0.0.1 is used to check, whether your local ssh command accepts the ControlPath option. 0.0.0.1 is a non-existing address; ssh shall return immediately with an error.
In more recent Tramp versions, the blocking is avoided by using the command ssh -o ConnectTimeout=1 -o ControlPath=%C 0.0.0.1. I recommend to upgrade ...
1. Download https://www.gnu.org/software/emacs/manual/info/elisp.info.gz to your /usr/share/info directory.
2. From a terminal run update-info-dir command.
3. From emacs C-h i m Elisp (capital E).