net-ipv6: bugfix - raw & sctp - switch to ipv6_can_nonlocal_bind()

Found by virtue of ipv6 raw sockets not honouring the per-socket
IP{,V6}_FREEBIND setting.

Based on hits found via:
  git grep '[.]ip_nonlocal_bind'
We fix both raw ipv6 sockets to honour IP{,V6}_FREEBIND and IP{,V6}_TRANSPARENT,
and we fix sctp sockets to honour IP{,V6}_TRANSPARENT (they already honoured
FREEBIND), and not just the ipv6 'ip_nonlocal_bind' sysctl.

The helper is defined as:
  static inline bool ipv6_can_nonlocal_bind(struct net *net, struct inet_sock *inet) {
    return net->ipv6.sysctl.ip_nonlocal_bind || inet->freebind || inet->transparent;
  }
so this change only widens the accepted opt-outs and is thus a clean bugfix.

I'm not entirely sure what 'fixes' tag to add, since this is AFAICT an ancient bug,
but IMHO this should be applied to stable kernels as far back as possible.
As such I'm adding a 'fixes' tag with the commit that originally added the helper,
which happened in 4.19.  Backporting to older LTS kernels (at ...