iptunnel: check SIT_ISATAP flag only for SIT tunnel

Without patch, I got:

	# ./ip/ip tunnel show
	ip_vti0: ioctl 89f4 failed: Invalid argument
	ip_vti0: ip/ip  remote any  local any  ttl inherit  nopmtudisc key 0

this is due to VTI_ISVTI has the same numeric value with SIT_ISATAP,
but only sit tunnel has SIOCGETPRL, therefore it should check for SIT
tunnel first.

Cc: Stephen Hemminger <stephen@networkplumber.org>
Signed-off-by: Cong Wang <amwang@redhat.com>

ip/iptunnel.c

@@ -341,7 +341,7 @@ static void print_tunnel(struct ip_tunnel_parm *p)
 	       p->iph.daddr ? format_host(AF_INET, 4, &p->iph.daddr, s1, sizeof(s1))  : "any",
 	       p->iph.saddr ? rt_addr_n2a(AF_INET, 4, &p->iph.saddr, s2, sizeof(s2)) : "any");
 
-	if (p->i_flags & SIT_ISATAP) {
+	if (p->iph.protocol == IPPROTO_IPV6 && (p->i_flags & SIT_ISATAP)) {
 		struct ip_tunnel_prl prl[16];
 		int i;