net: provide stubs for ip6_set_txhash and ip6_make_flowlabel

net: provide stubs for ip6_set_txhash and ip6_make_flowlabel

Commit cb1ce2ef387b ("ipv6: Implement automatic flow label generation
on transmit") introduced ip6_make_flowlabel, while commit b73c3d0e4f0e
("net: Save TX flow hash in sock and set in skbuf on xmit") introduced
ip6_set_txhash.

ip6_set_tx_hash() uses sk_v6_daddr which references
__sk_common.skc_v6_daddr from struct sock_common, which is gated with
IS_ENABLED(CONFIG_IPV6).

ip6_make_flowlabel() uses the ipv6 member from struct net which is
also gated with IS_ENABLED(CONFIG_IPV6).

When CONFIG_IPV6 is disabled, we will hit a build failure that looks
like this when the compiler attempts inlining these functions:

  CC [M]  drivers/net/ethernet/broadcom/bnx2x/bnx2x_main.o
In file included from include/net/inet_sock.h:27:0,
                 from include/net/ip.h:30,
                 from drivers/net/ethernet/broadcom/cnic.c:37:
include/net/ipv6.h: In function 'ip6_set_txhash':
include/net/sock.h:327:33: error: 'struct sock_common' has no member named 'skc_v6_daddr'
 #define sk_v6_daddr  __sk_common.skc_v6_daddr
                                 ^
include/net/ipv6.h:696:49: note: in expansion of macro 'sk_v6_daddr'
  keys.dst = (__force __be32)ipv6_addr_hash(&sk->sk_v6_daddr);
                                                 ^
In file included from include/net/inetpeer.h:15:0,
                 from include/net/route.h:28,
                 from include/net/ip.h:31,
                 from drivers/net/ethernet/broadcom/cnic.c:37:
include/net/ipv6.h: In function 'ip6_make_flowlabel':
include/net/ipv6.h:706:37: error: 'struct net' has no member named 'ipv6'
  if (!flowlabel && (autolabel || net->ipv6.sysctl.auto_flowlabels)) {
                                     ^

Fixes: cb1ce2ef387b ("ipv6: Implement automatic flow label generation on transmit")
Fixes: b73c3d0e4f0e ("net: Save TX flow hash in sock and set in skbuf on xmit")
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>