ipvs: fix build errors related to config option combinations

Fix two build error introduced by commit 63dca2c0:
 "ipvs: Fix faulty IPv6 extension header handling in IPVS"

First build error was fairly trivial and can occur, when
CONFIG_IP_VS_IPV6 is disabled.

The second build error was tricky, and can occur when deselecting
both all Netfilter and IPVS, but selecting CONFIG_IPV6.  This is
caused by "kernel/sysctl_binary.c" including "net/ip_vs.h", which
includes "linux/netfilter_ipv6/ip6_tables.h" causing include
of "include/linux/netfilter/x_tables.h" which then cannot find
the typedef nf_hookfn.

Fix this by only including "linux/netfilter_ipv6/ip6_tables.h" in
case of CONFIG_IP_VS_IPV6 as its already used to guard the usage
of ipv6_find_hdr().

Reported-by: Fengguang Wu <fengguang.wu@intel.com>
Reported-by: Yuanhan Liu <yuanhan.liu@linux.intel.com>
Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: Simon Horman <horms@verge.net.au>

include/net/ip_vs.h

@@ -22,7 +22,7 @@
 #include <linux/ip.h>
 #include <linux/ipv6.h>			/* for struct ipv6hdr */
 #include <net/ipv6.h>
-#if IS_ENABLED(CONFIG_IPV6)
+#if IS_ENABLED(CONFIG_IP_VS_IPV6)
 #include <linux/netfilter_ipv6/ip6_tables.h>
 #endif
 #if IS_ENABLED(CONFIG_NF_CONNTRACK)
@@ -212,8 +212,9 @@ ip_vs_fill_iph_addr_only(int af, const struct sk_buff *skb,
 			(struct ipv6hdr *)skb_network_header(skb);
 		iphdr->saddr.in6 = iph->saddr;
 		iphdr->daddr.in6 = iph->daddr;
-	} else {
+	} else
 #endif
+	{
 		const struct iphdr *iph =
 			(struct iphdr *)skb_network_header(skb);
 		iphdr->saddr.ip = iph->saddr;