Add missing header

[JWhitleyWork]

Not having this header has been causing build failures in rolling and won't hurt any earlier releases.

[xmfcx]

Rebased to test with the latest CI.

[xmfcx]

It still fails at the test for rolling but it at least builds now.

• https://github.com/autowarefoundation/ros2_socketcan/actions/runs/8437240909/job/23106598762?pr=42#step:5:531

Thanks @JWhitleyWork (I've also given you the write permissions for this repository since you have too much history in this package)

[JWhitleyWork]

Thanks, @xmfcx!