net: Include env.h in pcap.c

This file uses the environment but does not include the header file.
Update it.

Signed-off-by: Simon Glass <sjg@chromium.org>

net/pcap.c

@@ -3,6 +3,7 @@
  * Copyright 2019 Ramon Fried <rfried.dev@gmail.com>
  */
 
+#include <env.h>
 #include <net.h>
 #include <net/pcap.h>
 #include <time.h>