The patch should likely be first applied to upstream.

If the parent becomes a new persistent connection master daemon, stderr
of the proxy command should be detached, too, similar to the master
daemon's stderr, as changed in
openssh-portable@d2d6bf864e52af8491a60dd507f85b74361f5da3,
upstream@4fb726f0fdcb155ad419913cea10dc4afd409d24 and discussed in
bz#1988.

Signed-off-by: Steffen Prohaska <prohaska@zib.de>