nshlib: fix building when CONFIG_NET_USRSOCK enabled with other link-layer
#elif defined(CONFIG_NET_LOCAL)
# define NET_DEVNAME "lo"
# define NSH_HAVE_NETDEV
+#elif defined(CONFIG_NET_USRSOCK)
+# undef NSH_HAVE_NETDEV
#elif !defined(CONFIG_NET_LOOPBACK)
# error ERROR: No link layer protocol defined
#endif
