bug#28413: 26.0.50; enable frame filters for gdb-mi

[Eli Zaretskii]

> From: Tom Tromey <tom@tromey.com>
> Date: Sun, 10 Sep 2017 18:37:52 -0600
> 
> I noticed that gdb-mi doesn't enable frame filters.
> 
> I think it shouldn't hurt to simply always enable them, as in the
> attached patch.

Looks reasonable, thanks.