FreeBSD arm64 compile fails due to type mismatch

[feld]

Encountered while building the Deltachat-rpc-server:

error[E0308]: mismatched types
  --> /wrkdirs/usr/ports/net/deltachat-rpc-server/work/core-1.159.3/cargo-crates/netdev-0.31.0/src/interface/unix.rs:192:28
   |
192 |             let nlen: i8 = (*sa).sa_data[3];
   |                       --   ^^^^^^^^^^^^^^^^ expected `i8`, found `u8`
   |                       |
   |                       expected due to this
   |
help: you can convert a `u8` to an `i8` and panic if the converted value doesn't fit
   |
192 |             let nlen: i8 = (*sa).sa_data[3].try_into().unwrap();
   |                                            ++++++++++++++++++++

error[E0308]: mismatched types
  --> /wrkdirs/usr/ports/net/deltachat-rpc-server/work/core-1.159.3/cargo-crates/netdev-0.31.0/src/interface/unix.rs:193:28
   |
193 |             let alen: i8 = (*sa).sa_data[4];
   |                       --   ^^^^^^^^^^^^^^^^ expected `i8`, found `u8`
   |                       |
   |                       expected due to this
   |
help: you can convert a `u8` to an `i8` and panic if the converted value doesn't fit
   |
193 |             let alen: i8 = (*sa).sa_data[4].try_into().unwrap();
   |                                            ++++++++++++++++++++

The arm64 API defines char as unsigned which I believe is the root cause here: https://github.com/ARM-software/abi-aa/blob/main/aapcs64/aapcs64.rst#10arm-c-and-c-language-mappings

[shellrow]

Thank you!
We hadn’t tested on FreeBSD/arm64(only on x86_64).