Bluetooth: SCO: convert to getsockopt_iter

Convert SCO socket's getsockopt implementation to use the new
getsockopt_iter callback with sockopt_t.

Key changes:
- Replace (char __user *optval, int __user *optlen) with sockopt_t *opt
- Use opt->optlen for buffer length (input) and returned size (output)
- Use copy_to_iter() instead of put_user()/copy_to_user()
- Drop the open-coded ptr cursor in BT_CODEC; iter_out advances on
  every copy_to_iter() naturally
- Add linux/uio.h for copy_to_iter()

Signed-off-by: Breno Leitao <leitao@debian.org>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>