The midi events have their large data offsets relative to the start of
the buffer and the large data is at the end of the buffer. Because we
copied it down, right after the events, but we didn't adjust the
offsets, calculate a correction offset when unpacking the events.
SysEx in UMP can span multiple packets. In MIDI1 we can't split them up
into multiple events so we need to collect the complete sysex and then
write out the event.
Fixes SysEx writes to ALSA seq by running the event encoder until a
valid packet is completed.
Also fixes split MIDI1 packets in the JACK API when going through the
tunnel or via netjack.
This provides access to GNU C library-style endian and byteswap functions.
Windows doesn't provide pre-processor defines for endianness, but
all current Windows architectures (X32, X64, ARM) are little-endian.
