nshlib/nsh_console.c: Add fflush to nsh_consolewrite(). This resolves this problem:

> cat /dev/ttyCP &
  > echo ls >/dev/ttyCP

Can't get the 'ls' result immediately, because 'cat' cmd uses nsh_consolewrite() and that uses fwrite with no fflush. We can get the 'ls' result after type '\n', because nsh will fflush output when get '\n'.

nshlib/nsh_console.c

@@ -186,6 +186,11 @@ static ssize_t nsh_consolewrite(FAR struct nsh_vtbl_s *vtbl,
       _err("ERROR: [%d] Failed to send buffer: %d\n",
           pstate->cn_outfd, errno);
     }
+
+  /* Flush the data to the output stream */
+
+  fflush(pstate->cn_outstream);
+
   return ret;
 #else
   /* REVISIT: buffer may not be NUL-terminated */