Docs: Clarify that is_network_admin() does not check if the site is…

… a Multisite network; `is_multisite()` should be used for that.

Props svovaf, dilipbheda, tazotodua.
Fixes #47415.

git-svn-id: https://develop.svn.wordpress.org/trunk@45672 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/load.php

@@ -1031,6 +1031,9 @@ function is_blog_admin() {
  * Does not check if the user is an administrator; use current_user_can()
  * for checking roles and capabilities.
  *
+ * Does not check if the site is a Multisite network; use is_multisite()
+ * for checking if Multisite is enabled.
+ *
  * @since 3.1.0
  *
  * @global WP_Screen $current_screen