Add dhcp client config on usb network (depends on dhclient)

Signed-off-by: Philippe De Swert <philippedeswert@gmail.com>

docs/usb_moded-doc.txt

@@ -101,6 +101,7 @@ gateway = 10.0.0.1
 
 By default usb0 will be used, so no need to fill it in if not needed. The gateway setting is also optional
 and will not be set if there is no value filled in.
+If the ip is set to dhcp, usb_moded will try to use dhcp to configure the network (requires dhclient atm)
 
 Functional overview
 --------------------

src/usb_moded-network.c

@@ -23,6 +23,7 @@
 
 #include <stdio.h>
 #include <stdlib.h>
+#include <string.h>
 
 #include "usb_moded-network.h"
 #include "usb_moded-config.h"
@@ -79,6 +80,13 @@ int usb_network_up(void)
   	system("ifconfig usb0 192.168.2.15");
 	return(0);
   }
+  if(!strcmp(ip, "dhcp"))
+  {
+  	if(interface == NULL)
+		sprintf(command, "dhclient -d usb0\n");
+	else
+		sprintf(command, "dhclient -d %s\n", interface);
+  }
   if(interface == NULL)
 	sprintf(command, "ifconfig usb0 %s\n", ip);	
   else