pcbnew: Tune length of differential track get confused when pad to die differs

Description

Tune length of differential track shows total length of the trace + difference between pad to die values.

It should show total length of the longer of the tuned traces.

Steps to reproduce

1. Connect two components with differential pair.
2. Increase pad to die value in one of the pads to not equal second pad pad to die value.
3. Tune skew
4. Tune length of differential track shows total length of the trace + difference between pad to die values

KiCad Version

Application: KiCad PCB Editor

Version: 6.0.9-8da3e8f707~116~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 5.15.0-50-generic x86_64, 64 bit, Little endian, wxGTK, pantheon, x11

Build Info:
	Date: Oct 31 2022 20:18:12
	wxWidgets: 3.0.4 (wchar_t,wx containers,compatible with 2.8) GTK+ 3.24
	Boost: 1.71.0
	OCC: 7.5.2
	Curl: 7.86.0
	ngspice: 36
	Compiler: GCC 9.4.0 with C++ ABI 1013

Build settings:
	KICAD_USE_OCC=ON
	KICAD_SPICE=ON