Bluetooth: mgmt: Add support for setting the local name

This patch adds a new set_local_name management command as well as a
local_name_changed management event. With these user space can both
change the local name as well as monitor changes to it by others.

Signed-off-by: Johan Hedberg <johan.hedberg@nokia.com>
Signed-off-by: Gustavo F. Padovan <padovan@profusion.mobi>