Let the user bypass note on filtering when velocity is 0

Only for standalone program, dbus is not done yet.
See jackaudio/a2jmidid#14

(cherry picked from commit ee48ecee4d2cf2cd73ca29cbc2bf0b709de150fe)

a2jmidid.c

@@ -66,6 +66,7 @@ static bool g_started = false;
 struct a2j * g_a2j = NULL;
 size_t g_max_jack_port_name_size;
 bool g_disable_port_uniqueness = false;
+bool g_filter_note_on = true;
 
 bool g_a2j_export_hw_ports = false;
 char * g_a2j_jack_server_name = "default";
@@ -427,7 +428,7 @@ void
 a2j_help(
   const char * self)
 {
-  a2j_info("Usage: %s [-j jack-server] [-e | --export-hw] [-u]", self);
+  a2j_info("Usage: %s [-j jack-server] [-e | --export-hw] [-u] [-n]", self);
   a2j_info("Defaults:");
   a2j_info("-j default");
 }
@@ -485,6 +486,9 @@ main(
       case 'u':
         g_disable_port_uniqueness = true;
         break;
+      case 'n':
+        g_filter_note_on = false;
+        break;
       default:
         a2j_help(argv[0]);
         return 1;        

jack.c

@@ -36,6 +36,7 @@
 #include "port_thread.h"
 
 static bool g_freewheeling = false;
+extern bool g_filter_note_on;
 
 /*
  * =================== Input/output port handling =========================
@@ -176,7 +177,7 @@ a2j_input_event(
   }
 
   // fixup NoteOn with vel 0
-  if ((data[0] & 0xF0) == 0x90 && data[2] == 0x00) {
+  if (g_filter_note_on && (data[0] & 0xF0) == 0x90 && data[2] == 0x00) {
     data[0] = 0x80 + (data[0] & 0x0F);
     data[2] = 0x40;
   }

man/a2jmidid.1

@@ -3,7 +3,7 @@
 .SH NAME 
 a2jmidid \- JACK MIDI daemon for ALSA MIDI
 .SH SYNOPSIS
-.B a2jmidid [-j jack-server] [e | --export-hw]
+.B a2jmidid [-j jack-server] [e | --export-hw] [-u] [-n]
 .SH DESCRIPTION
 a2jmidid is a daemon that implements automatic bridging. For every ALSA
 sequencer port you get one JACK midi port. If ALSA sequencer port is
@@ -16,6 +16,8 @@ forces a2jmidid to bridge hardware ports as well as software ports
 forces a2jmidid to generate non-unique port names (see NOTES)
 .IP -j
 specifies which jack-server to use
+.IP -n
+do not filter note on
 .SH NOTES
 ALSA does not guarantee client names to by unique. I.e. it is possible
 to have two apps that create two clients with same ALSA client name.