ipv6: Refactor update of IPv6 flowi destination address for srcrt (RH) option

There are more than a dozen occurrences of following code in the
IPv6 stack:

    if (opt && opt->srcrt) {
            struct rt0_hdr *rt0 = (struct rt0_hdr *) opt->srcrt;
            ipv6_addr_copy(&final, &fl.fl6_dst);
            ipv6_addr_copy(&fl.fl6_dst, rt0->addr);
            final_p = &final;
    }

Replace those with a helper. Note that the helper overrides final_p
in all cases. This is ok as final_p was previously initialized to
NULL when declared.

Signed-off-by: Arnaud Ebalard <arno@natisbad.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/dccp/ipv6.c b/net/dccp/ipv6.c
index 0916988..6e3f325 100644
--- a/net/dccp/ipv6.c
+++ b/net/dccp/ipv6.c
@@ -248,7 +248,7 @@
 	struct ipv6_pinfo *np = inet6_sk(sk);
 	struct sk_buff *skb;
 	struct ipv6_txoptions *opt = NULL;
-	struct in6_addr *final_p = NULL, final;
+	struct in6_addr *final_p, final;
 	struct flowi fl;
 	int err = -1;
 	struct dst_entry *dst;
@@ -265,13 +265,7 @@
 
 	opt = np->opt;
 
-	if (opt != NULL && opt->srcrt != NULL) {
-		const struct rt0_hdr *rt0 = (struct rt0_hdr *)opt->srcrt;
-
-		ipv6_addr_copy(&final, &fl.fl6_dst);
-		ipv6_addr_copy(&fl.fl6_dst, rt0->addr);
-		final_p = &final;
-	}
+	final_p = fl6_update_dst(&fl, opt, &final);
 
 	err = ip6_dst_lookup(sk, &dst, &fl);
 	if (err)
@@ -545,19 +539,13 @@
 		goto out_overflow;
 
 	if (dst == NULL) {
-		struct in6_addr *final_p = NULL, final;
+		struct in6_addr *final_p, final;
 		struct flowi fl;
 
 		memset(&fl, 0, sizeof(fl));
 		fl.proto = IPPROTO_DCCP;
 		ipv6_addr_copy(&fl.fl6_dst, &ireq6->rmt_addr);
-		if (opt != NULL && opt->srcrt != NULL) {
-			const struct rt0_hdr *rt0 = (struct rt0_hdr *)opt->srcrt;
-
-			ipv6_addr_copy(&final, &fl.fl6_dst);
-			ipv6_addr_copy(&fl.fl6_dst, rt0->addr);
-			final_p = &final;
-		}
+		final_p = fl6_update_dst(&fl, opt, &final);
 		ipv6_addr_copy(&fl.fl6_src, &ireq6->loc_addr);
 		fl.oif = sk->sk_bound_dev_if;
 		fl.fl_ip_dport = inet_rsk(req)->rmt_port;
@@ -885,7 +873,7 @@
 	struct inet_sock *inet = inet_sk(sk);
 	struct ipv6_pinfo *np = inet6_sk(sk);
 	struct dccp_sock *dp = dccp_sk(sk);
-	struct in6_addr *saddr = NULL, *final_p = NULL, final;
+	struct in6_addr *saddr = NULL, *final_p, final;
 	struct flowi fl;
 	struct dst_entry *dst;
 	int addr_type;
@@ -988,13 +976,7 @@
 	fl.fl_ip_sport = inet->inet_sport;
 	security_sk_classify_flow(sk, &fl);
 
-	if (np->opt != NULL && np->opt->srcrt != NULL) {
-		const struct rt0_hdr *rt0 = (struct rt0_hdr *)np->opt->srcrt;
-
-		ipv6_addr_copy(&final, &fl.fl6_dst);
-		ipv6_addr_copy(&fl.fl6_dst, rt0->addr);
-		final_p = &final;
-	}
+	final_p = fl6_update_dst(&fl, np->opt, &final);
 
 	err = ip6_dst_lookup(sk, &dst, &fl);
 	if (err)