Style: use ngx_strlen() instead of strlen().

src/core/ngx_log.h

diff --git a/src/core/ngx_log.h b/src/core/ngx_log.h
index c1a52c4..95ecca5 100644
--- a/src/core/ngx_log.h
+++ b/src/core/ngx_log.h
@@ -248,7 +248,7 @@
 static ngx_inline void
 ngx_write_stderr(char *text)
 {
-    (void) ngx_write_fd(ngx_stderr, text, strlen(text));
+    (void) ngx_write_fd(ngx_stderr, text, ngx_strlen(text));
 }