net: Kconfig: add CONFIG_WGET symbol

Let net/wget.c and net/lwip/wget.c depend on CONFIG_WGET, and
cmd/wget.c depend on CONFIG_CMD_WGET. This way, the wget code
can be used regardless of whether the wget command is available.

Signed-off-by: Adriano Cordova <adrianox@gmail.com>
Reviewed-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
diff --git a/net/Makefile b/net/Makefile
index 209377a..7c917b3 100644
--- a/net/Makefile
+++ b/net/Makefile
@@ -29,7 +29,7 @@
 obj-$(CONFIG_CMD_WOL)  += wol.o
 obj-$(CONFIG_PROT_UDP) += udp.o
 obj-$(CONFIG_PROT_TCP) += tcp.o
-obj-$(CONFIG_CMD_WGET) += wget.o
+obj-$(CONFIG_WGET) += wget.o
 
 # Disable this warning as it is triggered by:
 # sprintf(buf, index ? "foo%d" : "foo", index)