[Bluetooth] Fix NULL pointer dereferences of the HCI socket

This patch fixes the two NULL pointer dereferences found by the sfuzz
tool from Ilja van Sprundel. The first one was a call of getsockname()
for an unbound socket and the second was calling accept() while this
operation isn't implemented for the HCI socket interface.

Signed-off-by: Marcel Holtmann <marcel@holtmann.org>