Bluetooth: Improve setsockopt() handling of malformed user input

The bt_copy_from_sockptr() return value is being misinterpreted by most
users: a non-zero result is mistakenly assumed to represent an error code,
but actually indicates the number of bytes that could not be copied.

Remove bt_copy_from_sockptr() and adapt callers to use
copy_safe_from_sockptr().

For sco_sock_setsockopt() (case BT_CODEC) use copy_struct_from_sockptr() to
scrub parts of uninitialized buffer.

Opportunistically, rename `len` to `optlen` in hci_sock_setsockopt_old()
and hci_sock_setsockopt().

Fixes: 51eda36d ("Bluetooth: SCO: Fix not validating setsockopt user input")
Fixes: a97de7bf ("Bluetooth: RFCOMM: Fix not validating setsockopt user input")
Fixes: 4f395124 ("Bluetooth: L2CAP: Fix not validating setsockopt user input")
Fixes: 9e8742cd ("Bluetooth: ISO: Fix not validating setsockopt user input")
Fixes: b2186061 ("Bluetooth: hci_sock: Fix not validating setsockopt user input")
Reviewed-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>
Reviewed-by: David Wei <dw@davidwei.uk>
Signed-off-by: Michal Luczaj <mhal@rbox.co>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>