acinclude: Also support pkg-config for configuring dpdk.

acinclude: Also support pkg-config for configuring dpdk.

If available use dpdk pkg-config info of libdpdk to set the right
include paths.
That for example, allows packagers to provide non default include
paths in a common way (pkg-config).

Signed-off-by: Christian Ehrhardt <christian.ehrhardt@canonical.com>
Suggested-by: Luca Boccassi <luca.boccassi@gmail.com>
Acked-by: Luca Boccassi <luca.boccassi@gmail.com>
Signed-off-by: Ben Pfaff <blp@ovn.org>