doc: migration guide: add note about IGMP migration

Added note about the migration steps needed to support the new IGMP api.
The api now expects an additional argument used for joining an IGMPv3
group.

Signed-off-by: Ibe Van de Veire <[email protected]>

Author: IVandeVeire

doc/releases/migration-guide-3.6.rst

@@ -139,6 +139,13 @@ Networking
   ``request`` argument for :c:func:`coap_well_known_core_get` is made ``const``.
   (:github:`64265`)
 
+* The IGMP multicast library now supports IGMPv3. This results in a minor change to the existing
+  api. The :c:func:`net_ipv4_igmp_join` now takes an additional argument of the type
+  ``const struct igmp_param *param``. This allows IGMPv3 to exclude/include certain groups of
+  addresses. If this functionality is not used or available (when using IGMPv2), you can safely pass
+  a NULL pointer. IGMPv3 can be enabled using the Kconfig ``CONFIG_NET_IPV4_IGMPV3``.
+  (:github:`65293`)
+
 Other Subsystems
 ================