net: ip6_gre: Split up ip6gre_tnl_change()

Split a reusable function ip6gre_tnl_copy_tnl_parm() from
ip6gre_tnl_change(). This will allow ERSPAN-specific code to
reuse the common parts while customizing the behavior for ERSPAN.

Fixes: 5a963eb61b7c ("ip6_gre: Add ERSPAN native tunnel support")
Signed-off-by: Petr Machata <petrm@mellanox.com>
Acked-by: William Tu <u9012063@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv6/ip6_gre.c

@@ -1112,8 +1112,8 @@ static void ip6gre_tnl_link_config(struct ip6_tnl *t, int set_mtu)
 	ip6gre_tnl_link_config_route(t, set_mtu, ip6gre_calc_hlen(t));
 }
 
-static int ip6gre_tnl_change(struct ip6_tnl *t,
-	const struct __ip6_tnl_parm *p, int set_mtu)
+static void ip6gre_tnl_copy_tnl_parm(struct ip6_tnl *t,
+				     const struct __ip6_tnl_parm *p)
 {
 	t->parms.laddr = p->laddr;
 	t->parms.raddr = p->raddr;
@@ -1129,6 +1129,12 @@ static int ip6gre_tnl_change(struct ip6_tnl *t,
 	t->parms.o_flags = p->o_flags;
 	t->parms.fwmark = p->fwmark;
 	dst_cache_reset(&t->dst_cache);
+}
+
+static int ip6gre_tnl_change(struct ip6_tnl *t, const struct __ip6_tnl_parm *p,
+			     int set_mtu)
+{
+	ip6gre_tnl_copy_tnl_parm(t, p);
 	ip6gre_tnl_link_config(t, set_mtu);
 	return 0;
 }