net/wireguard-kmod: Fix build on latest stable/13

PR: 256639
Obtained from: https://git.zx2c4.com/wireguard-freebsd/commit/?id=64a507ad6b3c7e8455c67b452160b9e4211fd872

(cherry picked from commit 57eb088f783473d1a7975d31a669d50b2f724e42)