annex: ssh control path outside of repo to fix sync of annex repos inside encfs mounts
matches control path in ~/.ssh/config
https://git.hammerle.me/fphammerle/config-openssh-user/commit/9c11b1a9afce3e5c53a5b8363f0fce3ed4be3479#diff-229ced76aa598665fade1eb7542d74c50586e34R11