MIDI: check range of port counts

Fuzz testing cause out-of-memory errors
when passing very large port counts.
Now we check to make sure the port count is in a resonable range.

Bug: 135639926
Test: any MIDI test will exercise this code
Test: https://source.android.com/devices/audio/midi_test.html
Change-Id: Ic5dedc1eda86ff86a73a1da66ee6630c9662ceb8