metrics: fix exported header

This commit addresses the following compilation errors:

 In file included from /tmp/check-includes.sh.21060.c:1:0:
 build/include/rte_metrics.h:91:2: error: unknown type name 'uint16_t'
 [...]

It also adds C++ awareness to rte_metrics.h.

Fixes: 349950ddb9c5 ("metrics: add information metrics library")

Signed-off-by: Adrien Mazarguil <adrien.mazarguil@6wind.com>
Acked-by: Remy Horton <remy.horton@intel.com>

lib/librte_metrics/rte_metrics.h

@@ -52,6 +52,12 @@
 #ifndef _RTE_METRICS_H_
 #define _RTE_METRICS_H_
 
+#include <stdint.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
 /** Maximum length of metric name (including null-terminator) */
 #define RTE_METRICS_MAX_NAME_LEN 64
 
@@ -237,4 +243,8 @@ int rte_metrics_update_values(
 	const uint64_t *values,
 	uint32_t count);
 
+#ifdef __cplusplus
+}
+#endif
+
 #endif