Footprint position generator dialog does not respect global units

Description

Both in the toolbar and in the properties units are set to millimeters, but default selection in Footprint position generator dialog is inches.

Steps to reproduce

1. Set mm as units in the toolbar
2. Set mm as units in preferences/pcbnew/editing options
3. Open Fabrication outputs/Footprint positions dialog
4. Units are selectes as Inches and selecting it to millimeters does not stick

KiCad Version

Application: Pcbnew

Version: 5.99.0-unknown-ba8b8d273~91~ubuntu20.04.1, release build

Libraries:
	wxWidgets 3.0.4
	libcurl/7.68.0 OpenSSL/1.1.1f zlib/1.2.11 brotli/1.0.7 libidn2/2.2.0 libpsl/0.21.0 (+libidn2/2.2.0) libssh/0.9.3/openssl/zlib nghttp2/1.40.0 librtmp/2.3

Platform: Linux 5.4.0-48-generic x86_64, 64 bit, Little endian, wxGTK, cinnamon, x11

Build Info:
	Date: Oct  4 2020 15:17:23
	wxWidgets: 3.0.4 (wchar_t,wx containers,compatible with 2.8) GTK+ 3.24
	Boost: 1.71.0
	OCE: 6.9.1
	Curl: 7.68.0
	ngspice: 31
	Compiler: GCC 9.3.0 with C++ ABI 1013

Build settings:
	KICAD_SCRIPTING=ON
	KICAD_SCRIPTING_MODULES=ON
	KICAD_SCRIPTING_PYTHON3=ON
	KICAD_SCRIPTING_WXPYTHON=ON
	KICAD_SCRIPTING_WXPYTHON_PHOENIX=ON
	KICAD_SCRIPTING_ACTION_MENU=ON
	BUILD_GITHUB_PLUGIN=ON
	KICAD_USE_OCE=ON
	KICAD_SPICE=ON