gnome-base/gdm: workaround file perm and bluetooth sound issues

gnome-base/gdm: workaround file perm and bluetooth sound issues

Install a pulseaudio default config file which unloads bluetooth modules,
to avoid logged in users failing to load these modules upon log-in due to
device locks. As bluetooth sound may be important for a11y screen reader
over bluetooth sound, a USE flag is provided to keep loading bluetooth
modules; as this shouldn't be a common case (especially as normal sound
still works, it's just about sound over bluetooth), this USE flag is
default disabled.

Add back file ownership tweaks, as users still somehow end up with
wrong permissions. At least if the path where Xorg sessions log file
gets written has wrong permissions, Xorg fails to start and gdm with it.

Bug: https://bugs.gentoo.org/679526
Closes: https://bugs.gentoo.org/669146
Package-Manager: Portage-2.3.62, Repoman-2.3.12
Signed-off-by: Mart Raudsepp <leio@gentoo.org>