make ngx_inet6_ntop() non-static

src/core/ngx_inet.h

diff --git a/src/core/ngx_inet.h b/src/core/ngx_inet.h
index f708c07..0b42abd 100644
--- a/src/core/ngx_inet.h
+++ b/src/core/ngx_inet.h
@@ -104,6 +104,7 @@
 in_addr_t ngx_inet_addr(u_char *text, size_t len);
 #if (NGX_HAVE_INET6)
 ngx_int_t ngx_inet6_addr(u_char *p, size_t len, u_char *addr);
+size_t ngx_inet6_ntop(u_char *p, u_char *text, size_t len);
 #endif
 size_t ngx_sock_ntop(struct sockaddr *sa, u_char *text, size_t len,
     ngx_uint_t port);