net: lwip: add dns command

Add CMD_DNS when NET_LWIP is enabled to provide the dns command using
lwIP.

Signed-off-by: Jerome Forissier <jerome.forissier@linaro.org>
Acked-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>

cmd/Kconfig

@@ -2027,11 +2027,6 @@ config CMD_SNTP
 	help
 	  Synchronize RTC via network
 
-config CMD_DNS
-	bool "dns"
-	help
-	  Lookup the IP of a hostname
-
 config CMD_LINK_LOCAL
 	bool "linklocal"
 	select LIB_RAND
@@ -2079,6 +2074,12 @@ config CMD_DHCP
 	help
 	  Boot image via network using DHCP/TFTP protocol
 
+config CMD_DNS
+	bool "dns"
+	select PROT_DNS_LWIP if NET_LWIP
+	help
+	  Lookup the IP of a hostname
+
 config CMD_MII
 	bool "mii"
 	imply CMD_MDIO

cmd/net-lwip.c

@@ -27,3 +27,11 @@ U_BOOT_CMD(
 	"[loadAddress] [[hostIPaddr:]bootfilename]"
 );
 #endif
+
+#if defined(CONFIG_CMD_DNS)
+U_BOOT_CMD(
+	dns,	3,	1,	do_dns,
+	"lookup the IP of a hostname",
+	"hostname [envvar]"
+);
+#endif