kni: add missing C++ guards

[ upstream commit e90df35c7a0328f7ad5bfc4d2d9968ff774d7f77 ]

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

Fixes: 3fc5ca2 ("kni: initial import")

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>

lib/librte_eal/linux/eal/include/rte_kni_common.h

@@ -6,6 +6,10 @@
 #ifndef _RTE_KNI_COMMON_H_
 #define _RTE_KNI_COMMON_H_
 
+#ifdef __cplusplus
+extern "C" {
+#endif
+
 #ifdef __KERNEL__
 #include <linux/if.h>
 #include <asm/barrier.h>
@@ -134,4 +138,8 @@ struct rte_kni_device_info {
 #define RTE_KNI_IOCTL_CREATE  _IOWR(0, 2, struct rte_kni_device_info)
 #define RTE_KNI_IOCTL_RELEASE _IOWR(0, 3, struct rte_kni_device_info)
 
+#ifdef __cplusplus
+}
+#endif
+
 #endif /* _RTE_KNI_COMMON_H_ */