net/local: fix blocking local sockets

Commit 4d6a8663fa made pipes and
named pipes block when opening for O_WRONLY or O_RDONLY. Local
sockets, however, require `local_open_client_tx` to be non-blocking
to enable the server side to prevent the server side from blocking.
If set otherwise, it would deadly block. This commit sets the FIFO
as non-blocking temporarily, open the TX side and, if originally
blocking - restores it to that state.

net/local/local_fifo.c

@@ -275,10 +275,9 @@ static int local_rx_open(FAR struct local_conn_s *conn, FAR const char *path,
 static int local_tx_open(FAR struct local_conn_s *conn, FAR const char *path,
                          bool nonblock)
 {
-  int oflags = nonblock ? O_WRONLY | O_NONBLOCK : O_WRONLY;
   int ret;
 
-  ret = file_open(&conn->lc_outfile, path, oflags);
+  ret = file_open(&conn->lc_outfile, path, O_WRONLY | O_NONBLOCK);
   if (ret < 0)
     {
       nerr("ERROR: Failed on open %s for writing: %d\n",
@@ -295,6 +294,17 @@ static int local_tx_open(FAR struct local_conn_s *conn, FAR const char *path,
       return ret == -ENOENT ? -EFAULT : ret;
     }
 
+  /* Clear O_NONBLOCK if it's meant to be blocking */
+
+  if (nonblock == false)
+    {
+      ret = file_fcntl(&conn->lc_outfile, F_SETFL, O_WRONLY);
+      if (ret < 0)
+        {
+          return ret;
+        }
+    }
+
   return OK;
 }