Function anonsocket_write

fn anonsocket_write<'tcx>(
    self_ref: FileDescriptionRef<AnonSocket>,
    ptr: Pointer,
    len: usize,
    ecx: &mut MiriInterpCx<'tcx>,
    finish: DynMachineCallback<'tcx, Result<usize, IoError>>,
) -> InterpResult<'tcx>

Write to AnonSocket based on the space available and return the written byte size.