mlx4: purge EOL release compatibility

Remove FreeBSD 10 support code.

Reviewed by: imp
Pull Request: https://github.com/freebsd/freebsd-src/pull/603
Differential Revision: https://reviews.freebsd.org/D35560

(cherry picked from commit 026babd427e6511e53478814ce0aa1cc3f7a9988)