bluetooth: Allow SCO socket packet size to be larger than mSBC frame

With USB Alternate Setting 3 size of HCI payload is 72 bytes which is already
larger than mSBC frame size. Largest known size of HCI payload is with USB
Alternate Setting 5 (144 bytes), make it the default SCO socket MTU.

Reserve additional space in bluetooth encoder buffer to cover this case.

Since mSBC encoder and decoder will now work with larger packet sizes, drop
assertions about MTU larger than mSBC frame size.

Part-of: <pulseaudio/pulseaudio!617>
2 jobs for pr/bluetooth-handle-large-sco-packet-size in 4 minutes and 23 seconds (queued for 8 seconds)