OS-3137 lxbrand pipe does not pollnotify when end is closed

@@ -612,13 +612,16 @@
         }
 
         /*
          * The other end of the pipe is almost closed so
          * reject any other open on this end of the pipe
-         * This only happens with a pipe mounted under namefs
+         * This normally only happens with a pipe mounted under namefs, but
+         * we can also see an open via proc/fd, which should still succeed.
+         * To indicate the proc/fd case the FKLYR flag is passed.
          */
-        if ((fnp->fn_flag & (FIFOCLOSE|ISPIPE)) == (FIFOCLOSE|ISPIPE)) {
+        if ((fnp->fn_flag & (FIFOCLOSE|ISPIPE)) == (FIFOCLOSE|ISPIPE) &&
+            (flag & FKLYR) == 0) {
                 fifo_cleanup(oldvp, flag);
                 cv_broadcast(&fnp->fn_wait_cv);
                 if (!lockheld)
                         mutex_exit(&fn_lock->flk_lock);
                 return (ENXIO);