Bluetooth: Use EOPNOTSUPP instead of ENOTSUPP

The EOPNOTSUPP and ENOTSUPP errors are very similar in meaning, but
ENOTSUPP is a fairly new addition to POSIX. Not all libc versions know
about the value the kernel uses for ENOTSUPP so it's better to use
EOPNOTSUPP to ensure understandable error messages.

Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>