I was sure I downloaded the 12.2 tree from the pfSense repo (https://github.com/pfsense/FreeBSD-src), anyway, I'm downloading the releng/12.2, and I'll patch with the igc driver.You downloaded the sources for 14.0-CURRENT (src-main.tar.gz, the main branch is -CURRENT).
If your machine has access to the internet simply use git(1):git clone -b releng/12.2 https://git.freebsd.org/src.git /usr/src
Or install net/gitup and use that to download the correct sources (don't forget the edit gitup.conf).
Branches: releng/13.0 = 13.0-RELEASE plus errata and security patches. releng/12.2 = 12.2-RELEASE plus errata and security patches.