Fix condition logic: The setup seems to support a network without sockets. That is not the case.

Squashed commit of the following:

    sched/sched/sched_getsockets.c:  Fix an error in conditional compilation.
    fs/:  Remove all conditional logic based on CONFIG_NSOCKET_DESCRIPTORS == 0
    Documentation/:  Remove all references to CONFIG_NSOCKET_DESCRIPTORS == 0
    include/:  Remove all conditional logic based on CONFIG_NSOCKET_DESCRIPTORS == 0
    libs/:  Remove all conditional logic based on CONFIG_NSOCKET_DESCRIPTORS == 0
    net/:  Remove all conditional logic based on CONFIG_NSOCKET_DESCRIPTORS == 0
    sched/:  Remove all conditional logic based on CONFIG_NSOCKET_DESCRIPTORS == 0
    syscall/:  Remove all conditional logic based on CONFIG_NSOCKET_DESCRIPTORS == 0
    tools/:  Fixups for CONFIG_NSOCKET_DESCRIPTORS no longer used to disable sockets.

include/nuttx/fs/fs.h

@@ -789,7 +789,7 @@ int file_dup(FAR struct file *filep, int minfd);
  *
  ****************************************************************************/
 
-#if defined(CONFIG_NET) && CONFIG_NSOCKET_DESCRIPTORS > 0
+#ifdef CONFIG_NET
 int fs_dupfd2(int fd1, int fd2);
 #else
 #  define fs_dupfd2(fd1, fd2) dup2(fd1, fd2)

include/nuttx/net/net.h

@@ -227,7 +227,7 @@ struct socket
 
 /* This defines a list of sockets indexed by the socket descriptor */
 
-#if CONFIG_NSOCKET_DESCRIPTORS > 0
+#ifdef CONFIG_NET
 struct socketlist
 {
   sem_t         sl_sem;      /* Manage access to the socket list */

include/nuttx/net/netdev.h

@@ -230,7 +230,7 @@ struct net_driver_s
    * Must be the first field in the structure due to blink type casting.
    */
 
-#if CONFIG_NSOCKET_DESCRIPTORS > 0
+#ifdef CONFIG_NET
   FAR struct net_driver_s *flink;
 
   /* This is the name of network device assigned when netdev_register was called.

include/nuttx/sched.h

@@ -544,7 +544,7 @@ struct task_group_s
 #endif
 #endif
 
-#if CONFIG_NSOCKET_DESCRIPTORS > 0
+#ifdef CONFIG_NET
   /* Sockets ********************************************************************/
 
   struct socketlist tg_socketlist;  /* Maps socket descriptor to socket         */
@@ -826,9 +826,9 @@ FAR struct filelist *sched_getfiles(void);
 FAR struct streamlist *sched_getstreams(void);
 #endif /* CONFIG_NFILE_STREAMS */
 
-#if CONFIG_NSOCKET_DESCRIPTORS > 0
+#ifdef CONFIG_NET
 FAR struct socketlist *sched_getsockets(void);
-#endif /* CONFIG_NSOCKET_DESCRIPTORS */
+#endif
 
 /********************************************************************************
  * Name: nxtask_starthook

include/sys/ioctl.h

@@ -45,7 +45,6 @@
 #include <nuttx/config.h>
 #include <nuttx/fs/ioctl.h>
 
-#if CONFIG_NSOCKET_DESCRIPTORS > 0
 #ifdef CONFIG_NET
 /* Include network IOCTL definitions */
 
@@ -77,7 +76,6 @@
 #  include <nuttx/wireless/ieee802154/ieee802154_mac.h>
 
 #endif /* CONFIG_WIRELESS_IEEE802154 */
-#endif /* CONFIG_NSOCKET_DESCRIPTORS > 0 */
 
 /****************************************************************************
  * Pre-processor Definitions

include/sys/syscall.h

@@ -270,11 +270,6 @@
  * enabled.
  */
 
-#ifndef CONFIG_NET
-#  undef CONFIG_NSOCKET_DESCRIPTORS
-#  define CONFIG_NSOCKET_DESCRIPTORS 0
-#endif
-
 #define SYS_close                    (__SYS_descriptors + 0)
 
 #ifdef CONFIG_LIBC_IOCTL_VARIADIC
@@ -524,7 +519,7 @@
 
 /* The following are defined only if networking AND sockets are supported */
 
-#if CONFIG_NSOCKET_DESCRIPTORS > 0
+#ifdef CONFIG_NET
 #  define SYS_accept                   (__SYS_network + 0)
 #  define SYS_bind                     (__SYS_network + 1)
 #  define SYS_connect                  (__SYS_network + 2)