BUG/MINOR: listener: Allow multiple "process" options on "bind" lines

BUG/MINOR: listener: Allow multiple "process" options on "bind" lines

The documentation specifies that you can have several "process" options to
define several ranges on "bind" lines (or "stats socket" lines). It is uncommon,
but it should be possible. So the bind_proc bitmask in bind_conf structure must
not be overwritten at each new "process" option parsed.

This bug also exists in 1.7, 1.6 and 1.5. So it may be backported. But no one
seems to have noticed it, so it was probably never hitted.