ipv6: introdcue __ipv6_addr_needs_scope_id and ipv6_iface_scope_id helper functions

[msm/android-3.4 commit 2c75b248e5243d0af7cc97522148db7415a70f8a]

__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

Bug: 9469865
Change-Id: I11213e9917223a6aefa243f541d1830c4234dda6
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>
Signed-off-by: Lorenzo Colitti <lorenzo@google.com>