bluez5: iso-io: track and apply corrections to tx latency

Use TX timestamps to get accurate reading of queue length and latency on kernel + controller side.

This is new kernel BT feature, so requires kernel with the necessary patches, available currently only in bluetooth-next/master branch. Enabling Poll Errqueue kernel experimental Bluetooth feature is also required for this.

Use the latency information to mitigate controller issues where ISO streams are desynchronized due to tx problems or spontaneously when some packets that should have been sent are left sitting in the queue, and transmission is off by a multiple of the ISO interval. This state is visible in the latency information, so if we see streams in a group have persistently different latencies, drop packets to resynchronize them.

Also make corrections if the kernel/controller queues get too long, so that we don't have too big latency there.

Since BlueZ watches the same socket for errors, and TX timestamps arrive via the socket error queue, we need to set BT_POLL_ERRQUEUE in addition to SO_TIMESTAMPING so that BlueZ doesn't think TX timestamps are errors.

Link: https://github.com/bluez/bluez/issues/515 Link: https://lore.kernel.org/linux-bluetooth/cover.1710440392.git.pav@iki.fi/ Link: https://lore.kernel.org/linux-bluetooth/f57e065bb571d633f811610d273711c7047af335.1712499936.git.pav@iki.fi/