BUG/MEDIUM: config: propagate frontend to backend process binding again.

This basically reverts 3507d5d ("MEDIUM: proxy: only adjust the backend's
bind-process when already set"). It was needed during the transition to
the new process binding method but is causing trouble now because frontend
to backend binding is not properly propagated.

This fix should be backported to 1.5.
(cherry picked from commit 8a3478ed31a16904f45178c153f4649faf6de675)
1 file changed