samples: net: dumb_http_server: Add net_pkt.h file inclusion

The function net_pkt_get_info() is found in net_pkt.h and not
in buf.h. This caused
"implicit declaration of function ‘net_pkt_get_info’"
warning if CONFIG_NET_BUF_POOL_USAGE was enabled.

Signed-off-by: Jukka Rissanen <[email protected]>

Author: jukkar

samples/net/sockets/dumb_http_server/src/socket_dumb_http.c

@@ -20,7 +20,7 @@
 #include <net/socket.h>
 #include <kernel.h>
 
-#include <net/buf.h>
+#include <net/net_pkt.h>
 
 #endif