fix: remove Netlink error variant for Android

[link2xt]

This fixes compilation of Delta Chat
in debug mode
for Android 5 (API level 21) using NDK 27.
Without this change symbols like
process_vm_writev which are not
actually used are pulled in
and break linking step.
They are only optimized out
in release mode.

See chatmail/core#6687
for details.

[link2xt]

CI is testing the build for Android, but not the linking of any binary, maybe that is why it was not detected.

[flub]

I thought our CI was compiling for android? We need to figure out why that wasn't working.

[dignifiedquire]

hmm, not sure this is the right fix, rtnetlink is used on android, and the regression was in that crate, which is why we pinned to an older version, as the newer versions do not compile on android asfaict.

[link2xt]

The problem is not that it does not compile, but that exporting an error variant from a crate results in the compiler including unused unrelated functions from nix package and stdlib that use C symbols not available on Android. These functions are optimized out in release mode. This is not related to previous problems with new rtnetlink not compiling.

[link2xt]

I thought our CI was compiling for android? We need to figure out why that wasn't working.

CI runs cargo build which is not enough - in the end you also need to link against bionic libc from the NDK and this is where it fails because some libc functions are not available.

[link2xt]

hmm, not sure this is the right fix

I don't think there is a proper fix - sufficiently dumb compiler can throw the whole libc in without removing any unused symbols and then it will not link. But at least this change fixes our setup for now.

[dignifiedquire]

the state of (handling) android is horrible, so if this works, lets just use it for now