This reverts commit 8702ff2189,
and b10d9cf09b.
There was a misconception on the iterator (port vs message
in sequence), besides Ardour's mixer-strip is preferably used
with a single MIDI port. Most plugin-standards also only support
one port.
If need be LuaDSP run_map() can be used to handle multiple
MIDI I/O ports already.
1d17993a29