ALSA: seq: oss: Send fragmented SysEx messages immediately

The recent bug report spotted on the old OSS sequencer code that tries
to combine incoming SysEx messages to a single sequencer event.  This
is good, per se, but it has more demerits:

- The sysex message delivery is delayed until the very last event
- The use of internal buffer forced the serialization

The recent fix in commit 0179488c ("ALSA: seq: oss: Fix races at
processing SysEx messages") addressed the latter, but a better fix is
to handle the sysex messages immediately, i.e. just send each incoming
fragmented sysex message as is.  And this patch implements that.
This resulted in a significant cleanup as well.

Note that the only caller of snd_seq_oss_synth_sysex() is
snd_seq_oss_process_event(), and all its callers dispatch the event
immediately, so we can just put the passed buffer pointer to the event
record to be handled.

Reported-and-tested-by: Kun Hu <huk23@m.fudan.edu.cn>
Link: https://lore.kernel.org/2B7E93E4-B13A-4AE4-8E87-306A8EE9BBB7@m.fudan.edu.cn
Link: https://patch.msgid.link/20241231115523.15796-1-tiwai@suse.de


Signed-off-by: Takashi Iwai <tiwai@suse.de>