mlx4: remove no longer needed header

Remove linux/inetdevice.h as neither of the two inline functions there
are used here.

Sposored by: The FreeBSD Foundation
Reviewed by: hselasky
Differential Revision: https://reviews.freebsd.org/D29428

(cherry picked from commit 5a461a86cf5bb0ac4ffde3caf03df0386ddad6cc)