global: Avoid indirect inclusion of <env.h> from <net.h>

Now that env_get_ip() has been removed, the include file <net.h> does
not need anything from <env.h>. Furthermore, include/env.h itself
includes other headers which can lead to longer indirect inclusion
paths. To prepare to remove <env.h> from <net.h> fix all of the
remaining places which had relied on this indirect inclusion to instead
include <env.h> directly.

Reviewed-by: Jerome Forissier <jerome.forissier@linaro.org> # net/lwip
Acked-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Reviewed-by: Wolfgang Wallner <wolfgang.wallner@br-automation.com>
Reviewed-by: Martyn Welch <martyn.welch@collabora.com>
Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/net/lwip/dhcp.c b/net/lwip/dhcp.c
index 92bd706..043d2ab 100644
--- a/net/lwip/dhcp.c
+++ b/net/lwip/dhcp.c
@@ -3,6 +3,7 @@
 
 #include <command.h>
 #include <console.h>
+#include <env.h>
 #include <log.h>
 #include <dm/device.h>
 #include <linux/delay.h>