ipv6: introdcue __ipv6_addr_needs_scope_id and ipv6_iface_scope_id helper functions

__ipv6_addr_needs_scope_id checks if an ipv6 address needs to supply
a 'sin6_scope_id != 0'. 'sin6_scope_id != 0' was enforced in case
of link-local addresses. To support interface-local multicast these
checks had to be enhanced and are now consolidated into these new helper
functions.

v2:
a) migrated to struct ipv6_addr_props

v3:
a) reverted changes for ipv6_addr_props
b) test for address type instead of comparing scope

v4:
a) unchanged

Suggested-by: YOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>
Cc: YOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>
Acked-by: YOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>
Signed-off-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
Acked-by: YOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/ipv6.h

@@ -320,6 +320,18 @@ static inline int ipv6_addr_src_scope(const struct in6_addr *addr)
 	return __ipv6_addr_src_scope(__ipv6_addr_type(addr));
 }
 
+static inline bool __ipv6_addr_needs_scope_id(int type)
+{
+	return type & IPV6_ADDR_LINKLOCAL ||
+	       (type & IPV6_ADDR_MULTICAST &&
+		(type & (IPV6_ADDR_LOOPBACK|IPV6_ADDR_LINKLOCAL)));
+}
+
+static inline __u32 ipv6_iface_scope_id(const struct in6_addr *addr, int iface)
+{
+	return __ipv6_addr_needs_scope_id(__ipv6_addr_type(addr)) ? iface : 0;
+}
+
 static inline int ipv6_addr_cmp(const struct in6_addr *a1, const struct in6_addr *a2)
 {
 	return memcmp(a1, a2, sizeof(struct in6_addr));