benchtests: Add IPv6 inet_ntop benchmark

Random IP addresses in the full range.  There is no extra workload
to check the effectiveness '::' optimization for a set of 0-oct
sets (although it would be a possible workload).
Reviewed-by: DJ Delorie <dj@redhat.com>

benchtests/Makefile

@@ -162,6 +162,7 @@ bench-pthread := \
 
 bench-resolv := \
   inet_ntop_ipv4 \
+  inet_ntop_ipv6 \
   # bench-resolv
 
 LDLIBS-bench-pthread-mutex-lock += -lm

benchtests/inet_ntop_ipv6-source.c

@@ -0,0 +1,10 @@
+#include <arpa/inet.h>
+#include <stdint.h>
+
+static void
+inet_ntop_ipv6 (uint32_t addr1, uint32_t addr2, uint32_t addr3, uint32_t addr4)
+{
+  struct in6_addr saddr = { .s6_addr32 = { addr1, addr2, addr3, addr4 } };
+  char dst[INET6_ADDRSTRLEN];
+  inet_ntop (AF_INET6, &saddr, dst, sizeof dst);
+}