sntp: use udp framework

This commits update the support of sntp to use
the framework udp. This change allows to remove
all the reference to sntp in the main network
file net/net.c.

Signed-off-by: Philippe Reynes <philippe.reynes@softathome.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/cmd/Kconfig b/cmd/Kconfig
index 30c358d..999b6cf 100644
--- a/cmd/Kconfig
+++ b/cmd/Kconfig
@@ -1645,6 +1645,7 @@
 
 config CMD_SNTP
 	bool "sntp"
+	select PROT_UDP
 	help
 	  Synchronize RTC via network
 
diff --git a/cmd/net.c b/cmd/net.c
index 9bbcdbc..beb2877 100644
--- a/cmd/net.c
+++ b/cmd/net.c
@@ -13,6 +13,8 @@
 #include <env.h>
 #include <image.h>
 #include <net.h>
+#include <net/udp.h>
+#include <net/sntp.h>
 
 static int netboot_common(enum proto_t, struct cmd_tbl *, int, char * const []);
 
@@ -356,6 +358,12 @@
 #endif
 
 #if defined(CONFIG_CMD_SNTP)
+static struct udp_ops sntp_ops = {
+	.prereq = sntp_prereq,
+	.start = sntp_start,
+	.data = NULL,
+};
+
 int do_sntp(struct cmd_tbl *cmdtp, int flag, int argc, char *const argv[])
 {
 	char *toff;
@@ -380,7 +388,7 @@
 	else
 		net_ntp_time_offset = simple_strtol(toff, NULL, 10);
 
-	if (net_loop(SNTP) < 0) {
+	if (udp_loop(&sntp_ops) < 0) {
 		printf("SNTP failed: host %pI4 not responding\n",
 		       &net_ntp_server);
 		return CMD_RET_FAILURE;