doc: Document network task affinity option

doc/networking/networkapp.t

@@ -101,6 +101,11 @@ struct rtems_bsdnet_config @{
   unsigned long        tcp_tx_buf_size;
   /* TCP TX: 16 * 1024 bytes */
   unsigned long        tcp_rx_buf_size;
+  /* Default Network Tasks CPU Affinity */
+#ifdef RTEMS_SMP
+  const cpu_set_t     *network_task_cpuset;
+  size_t               network_task_cpuset_size;
+#endif
 @};
 @end group
 @end example
@@ -229,6 +234,15 @@ This configuration parameter specifies the maximum amount of
 buffer memory which may be used for TCP sockets to receive
 into.  The default size is sixteen kilobytes.
 
+@item const cpu_set_t *network_task_cpuset
+This configuration parameter specifies the CPU affinity of the
+network task. If set to @code{0} the network task can be scheduled on
+any CPU. Only available in SMP configurations.
+
+@item size_t network_task_cpuset_size
+This configuration parameter specifies the size of the
+@code{network_task_cpuset} used. Only available in SMP configurations.
+
 @end table
 
 In addition, the following fields in the @code{rtems_bsdnet_ifconfig}