ipv6: Fix crash when IPv6 is administratively disabled

ipv6: Fix crash when IPv6 is administratively disabled

The global 'raw_v6_hashinfo' variable can be accessed even when IPv6 is
administratively disabled via the 'ipv6.disable=1' kernel command line
option, leading to a crash [1].

Fix by restoring the original behavior and always initializing the
variable, regardless of IPv6 support being administratively disabled or
not.

[1]
 BUG: unable to handle page fault for address: ffffffffffffffc8
 #PF: supervisor read access in kernel mode
 #PF: error_code(0x0000) - not-present page
 PGD 173e18067 P4D 173e18067 PUD 173e1a067 PMD 0
 Oops: 0000 [#1] PREEMPT SMP KASAN
 CPU: 3 PID: 271 Comm: ss Not tainted 6.0.0-rc4-custom-00136-g0727a9a5fbc1 #1396
 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.0-1.fc36 04/01/2014
 RIP: 0010:raw_diag_dump+0x310/0x7f0
 [...]
 Call Trace:
  <TASK>
  __inet_diag_dump+0x10f/0x2e0
  netlink_dump+0x575/0xfd0
  __netlink_dump_start+0x67b/0x940
  inet_diag_handler_cmd+0x273/0x2d0
  sock_diag_rcv_msg+0x317/0x440
  netlink_rcv_skb+0x15e/0x430
  sock_diag_rcv+0x2b/0x40
  netlink_unicast+0x53b/0x800
  netlink_sendmsg+0x945/0xe60
  ____sys_sendmsg+0x747/0x960
  ___sys_sendmsg+0x13a/0x1e0
  __sys_sendmsg+0x118/0x1e0
  do_syscall_64+0x34/0x80
  entry_SYSCALL_64_after_hwframe+0x63/0xcd

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Fixes: 0daf07e52709 ("raw: convert raw sockets to RCU")
Reported-by: Roberto Ricci <rroberto2r@gmail.com>
Tested-by: Roberto Ricci <rroberto2r@gmail.com>
Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Reviewed-by: David Ahern <dsahern@kernel.org>
Link: https://lore.kernel.org/r/20220916084821.229287-1-idosch@nvidia.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>