net: bootp: Fix compile error processing ntpserver option

When the following configuration is set

  # CONFIG_CMD_DHCP is not set
  CONFIG_CMD_BOOTP=y
  CONFIG_BOOTP_NTPSERVER=y

The following compile error is observed

  error: used struct type value where scalar is required
    if (net_ntp_server)
        ^~~~~~~~~~~~~~

Resolve this by checking net_ntp_server.s_addr instead.

Signed-off-by: Chris Packham <judge.packham@gmail.com>
Acked-by: Joe Hershberger <joe.hershberger@ni.com>

net/bootp.c

@@ -333,7 +333,7 @@ static void bootp_process_vendor(u8 *ext, int size)
 		debug("net_nis_domain : %s\n", net_nis_domain);
 
 #if defined(CONFIG_CMD_SNTP) && defined(CONFIG_BOOTP_NTPSERVER)
-	if (net_ntp_server)
+	if (net_ntp_server.s_addr)
 		debug("net_ntp_server : %pI4\n", &net_ntp_server);
 #endif
 }