Bluetooth: hidp: Fix regression with older userspace and flags validation

While it is not used by newer userspace anymore, the older userspace was
utilizing HIDP_VIRTUAL_CABLE_UNPLUG and HIDP_BOOT_PROTOCOL_MODE flags
when adding a new HIDP connection.

The flags validation is important, but we can not break older userspace
and with that allow providing these flags even if newer userspace does
not use them anymore.

Reported-and-tested-by: Jörg Otte <jrg.otte@gmail.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>