ipvlan: ensure network headers are in skb linear part

ipvlan: ensure network headers are in skb linear part

syzbot found that ipvlan_process_v6_outbound() was assuming
the IPv6 network header isis present in skb->head [1]

Add the needed pskb_network_may_pull() calls for both
IPv4 and IPv6 handlers.

[1]
BUG: KMSAN: uninit-value in __ipv6_addr_type+0xa2/0x490 net/ipv6/addrconf_core.c:47
  __ipv6_addr_type+0xa2/0x490 net/ipv6/addrconf_core.c:47
  ipv6_addr_type include/net/ipv6.h:555 [inline]
  ip6_route_output_flags_noref net/ipv6/route.c:2616 [inline]
  ip6_route_output_flags+0x51/0x720 net/ipv6/route.c:2651
  ip6_route_output include/net/ip6_route.h:93 [inline]
  ipvlan_route_v6_outbound+0x24e/0x520 drivers/net/ipvlan/ipvlan_core.c:476
  ipvlan_process_v6_outbound drivers/net/ipvlan/ipvlan_core.c:491 [inline]
  ipvlan_process_outbound drivers/net/ipvlan/ipvlan_core.c:541 [inline]
  ipvlan_xmit_mode_l3 drivers/net/ipvlan/ipvlan_core.c:605 [inline]
  ipvlan_queue_xmit+0xd72/0x1780 drivers/net/ipvlan/ipvlan_core.c:671
  ipvlan_start_xmit+0x5b/0x210 drivers/net/ipvlan/ipvlan_main.c:223
  __netdev_start_xmit include/linux/netdevice.h:5150 [inline]
  netdev_start_xmit include/linux/netdevice.h:5159 [inline]
  xmit_one net/core/dev.c:3735 [inline]
  dev_hard_start_xmit+0x247/0xa20 net/core/dev.c:3751
  sch_direct_xmit+0x399/0xd40 net/sched/sch_generic.c:343
  qdisc_restart net/sched/sch_generic.c:408 [inline]
  __qdisc_run+0x14da/0x35d0 net/sched/sch_generic.c:416
  qdisc_run+0x141/0x4d0 include/net/pkt_sched.h:127
  net_tx_action+0x78b/0x940 net/core/dev.c:5484
  handle_softirqs+0x1a0/0x7c0 kernel/softirq.c:561
  __do_softirq+0x14/0x1a kernel/softirq.c:595
  do_softirq+0x9a/0x100 kernel/softirq.c:462
  __local_bh_enable_ip+0x9f/0xb0 kernel/softirq.c:389
  local_bh_enable include/linux/bottom_half.h:33 [inline]
  rcu_read_unlock_bh include/linux/rcupdate.h:919 [inline]
  __dev_queue_xmit+0x2758/0x57d0 net/core/dev.c:4611
  dev_queue_xmit include/linux/netdevice.h:3311 [inline]
  packet_xmit+0x9c/0x6c0 net/packet/af_packet.c:276
  packet_snd net/packet/af_packet.c:3132 [inline]
  packet_sendmsg+0x93e0/0xa7e0 net/packet/af_packet.c:3164
  sock_sendmsg_nosec net/socket.c:718 [inline]

Fixes: 2ad7bf363841 ("ipvlan: Initial check-in of the IPVLAN driver.")
Reported-by: syzbot+93ab4a777bafb9d9f960@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/netdev/67b74f01.050a0220.14d86d.02d8.GAE@google.com/T/#u
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Mahesh Bandewar <maheshb@google.com>
Link: https://patch.msgid.link/20250220155336.61884-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>