fs: nfs: Introduce CONFIG_NFS_DONT_BIND_TCP_SOCKET

Summary:
- Some network drivers such as GS2200M do not support to bind
  a local port for TCP client socket. In this case, this config
  disables to bind the port.
- See also https://github.com/apache/nuttx/pull/3707

Impact:
- None

Testing:
- Tested with spresense:wifi_smp (Kconfig will be updated later)
- Tested with sabre-6quad:netnsh_smp (QEMU)

Signed-off-by: Masayuki Ishikawa <Masayuki.Ishikawa@jp.sony.com>

fs/nfs/Kconfig

@@ -13,6 +13,15 @@ config NFS
 
 #if NFS
 
+config NFS_DONT_BIND_TCP_SOCKET
+	bool
+	default n
+	depends on NFS
+	---help---
+		Some network drivers such as GS2200M do not support to bind
+		a local port for TCP client socket. In this case, this config
+		disables to bind the port.
+
 config NFS_STATISTICS
 	bool "NFS Statistics"
 	default n

fs/nfs/rpc_clnt.c

@@ -240,6 +240,13 @@ static int rpcclnt_socket(FAR struct rpcclnt *rpc, in_port_t rport)
       goto bad;
     }
 
+#ifdef CONFIG_NFS_DONT_BIND_TCP_SOCKET
+  if (rpc->rc_sotype == SOCK_STREAM)
+    {
+      goto connect;
+    }
+#endif
+
   /* Some servers require that the client port be a reserved port
    * number. We always allocate a reserved port, as this prevents
    * filehandle disclosure through UDP port capture.
@@ -263,6 +270,10 @@ static int rpcclnt_socket(FAR struct rpcclnt *rpc, in_port_t rport)
       goto bad;
     }
 
+#ifdef CONFIG_NFS_DONT_BIND_TCP_SOCKET
+connect:
+#endif
+
   /* Protocols that do not require connections could be optionally left
    * unconnected.  That would allow servers to reply from a port other than
    * the NFS_PORT.