net: Add a function to run dhcp

At present this must be done by executing the command. Also it involves
fiddling with the environment to determine the correct autoload behaviour.

Ideally it should be possible to run network operations without even
having the command line present (CONFIG_CMDLINE).

For now, add a function to handle DHCP, so it can be called from a bootdev
more easily.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Ramon Fried <rfried.dev@gmail.com>

include/net.h

@@ -65,6 +65,21 @@ struct in_addr {
  */
 int do_tftpb(struct cmd_tbl *cmdtp, int flag, int argc, char *const argv[]);
 
+/**
+ * dhcp_run() - Run DHCP on the current ethernet device
+ *
+ * This sets the autoload variable, then puts it back to similar to its original
+ * state (y, n or unset).
+ *
+ * @addr: Address to load the file into (0 if @autoload is false)
+ * @fname: Filename of file to load (NULL if @autoload is false or to use the
+ * default filename)
+ * @autoload: true to load the file, false to just get the network IP
+ * @return 0 if OK, -EINVAL if the environment failed, -ENOENT if ant file was
+ * not found
+ */
+int dhcp_run(ulong addr, const char *fname, bool autoload);
+
 /**
  * An incoming packet handler.
  * @param pkt    pointer to the application packet