ethdev: add missing C++ guards

ethdev: add missing C++ guards

Some public header files were missing 'extern "C"' C++ guards,
and couldn't be used by C++ applications. Add the missing guards.

Fixes: 7a3f27cbf59b ("ethdev: add access to specific device info")
Fixes: dcd5c8112bc3 ("ethdev: add PCI driver helpers")
Fixes: 7f0a669e7b04 ("ethdev: add allocation helper for virtual drivers")
Fixes: 7a3357205755 ("lib: remove C++ include guard from private headers")
Cc: stable@dpdk.org
Signed-off-by: Brian Dooley <brian.dooley@intel.com>
Acked-by: Bruce Richardson <bruce.richardson@intel.com>
Acked-by: Tyler Retzlaff <roretzla@linux.microsoft.com>