net/dpdk: Fix build after r347984

Address missing implicit includes removed as a header pollution cleanup in
r347984. Apologies that this wasn't addressed in advance; my spot check
ahead of time seems to have been against the wrong kernel source tree.

I have submitted the same changes to upstream dpdk:

https://bugs.dpdk.org/show_bug.cgi?id=282

Reviewed by: mat
Approved by: mat
Differential Revision: https://reviews.freebsd.org/D20329