geneve: Introduce IFLA_GENEVE_LOCAL and IFLA_GENEVE_LOCAL6.

By default, a GENEVE device bind()s its underlying UDP socket(s) to
the IPv4 or IPv6 wildcard address because there is no way to specify
a specific local IP address to bind() to.

This prevents deploying multiple GENEVE devices on a multi-homed host
where each device should be isolated and bound to a different local IP
address on the same UDP port.

Let's introduce new options, IFLA_GENEVE_LOCAL and IFLA_GENEVE_LOCAL6,
to allow specifying a local IPv4/IPv6 address for the backend UDP
socket.

By default, when collect metadata mode (IFLA_GENEVE_COLLECT_METADATA)
is enabled, both IPv4 and IPv6 sockets are created.  However, if a
source address is specified via the new attributes, only a single
socket corresponding to that specific address family is created.

Accordingly, geneve_find_sock() and geneve_find_dev() are updated to
take the source address into account, ensuring that multiple devices
and sockets configured with different source addresses can coexist
without conflict.

In addition, the source address is validated in geneve_xmit_skb()
and geneve6_xmit_skb(), so the BPF prog must set it in bpf_tunnel_key.

With this change, multiple GENEVE devices can be successfully created
and bound to their respective local IP addresses:

  (*) "local" is the keyword for IFLA_GENEVE_LOCAL / IFLA_GENEVE_LOCAL6

  # for i in $(seq 1 2);
  do
          ip link add geneve4_${i} type geneve local 192.168.0.${i} external
          ip addr add 192.168.0.${i}/24 dev geneve4_${i}
          ip link set geneve4_${i} up

          ip link add geneve6_${i} type geneve local 2001:9292::${i} external
          ip addr add 2001:9292::${i}/64 dev geneve6_${i} nodad
          ip link set geneve6_${i} up
  done

  # ip -d l | grep geneve
  9: geneve4_1: <BROADCAST,MULTICAST,UP,LOWER_UP> ...
      geneve external id 0 local 192.168.0.1 ...
  10: geneve6_1: <BROADCAST,MULTICAST,UP,LOWER_UP> ...
      geneve external id 0 local 2001:9292::1 ...
  11: geneve4_2: <BROADCAST,MULTICAST,UP,LOWER_UP> ...
      geneve external id 0 local 192.168.0.2 ...
  12: geneve6_2: <BROADCAST,MULTICAST,UP,LOWER_UP> ...
      geneve external id 0 local 2001:9292::2 ...

  # ss -ua | grep geneve
  UNCONN 0      0         192.168.0.2:geneve      0.0.0.0:*
  UNCONN 0      0         192.168.0.1:geneve      0.0.0.0:*
  UNCONN 0      0      [2001:9292::2]:geneve            *:*
  UNCONN 0      0      [2001:9292::1]:geneve            *:*

Note that even if the local address is explicitly configured with
the wildcard address, kernel does not dump it except for devices with
IFLA_GENEVE_COLLECT_METADATA.  This is consistent with the behaviour
of is_tnl_info_zero(), which treats the wildcard remote address as not
configured.

  ## ynl example.
  # ./tools/net/ynl/pyynl/cli.py \
    --spec ./Documentation/netlink/specs/rt-link.yaml \
    --do newlink --create \
    --json '{"ifname": "geneve0",
             "linkinfo": {"kind":"geneve",
	                  "data": {"local": "0.0.0.0",
			           "collect-metadata": true}}}'

  # ./tools/net/ynl/pyynl/cli.py \
    --spec ./Documentation/netlink/specs/rt-link.yaml \
    --do getlink \
    --json '{"ifname": "geneve0"}' --output-json | \
    jq .linkinfo.data.local
  "0.0.0.0"

Signed-off-by: Kuniyuki Iwashima <kuniyu@google.com>
Link: https://patch.msgid.link/20260602190436.139591-6-kuniyu@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>