This allows arm64 to pull armhf images.
Before this change the transfer service would reject pulls for armhf on
an arm64 machine, or indeed any such platform variant mismatches.
I would argue that its a bit weird for the transfer service to reject a
pull at all since there are legitamate reasons to want to pull images
for other architectures, however that's a more philosophical change.
In the case where I ran into this, I have an arm64 machine running
an armhf containerd in an armhf container (for running some basic sanity
checks during packaging).
Tests started failing once `ctr` was moved to use the transfer service
by default.
Signed-off-by: Brian Goff <cpuguy83@gmail.com>