INTERFACES TO LEAVE/JOIN IGMP MULTICAST GROUP

```
Description: The interfaces used to leave/join IGMP multicast groups is non-standard.
RFC3678 (IGMPv3) suggests ioctl() commands to do this (SIOCSIPMSFILTER) but
also status that those APIs are historic. NuttX implements these ioctl
commands, but is non-standard because: (1) It does not support IGMPv3, and
(2) it looks up drivers by their device name (e.g., "eth0") vs IP address.

Linux uses setsockopt() to control multicast group membership using the
IP_ADD_MEMBERSHIP and IP_DROP_MEMBERSHIP options. It also looks up drivers
using IP addresses (It would require additional logic in NuttX to look up
drivers by IP address). See http://tldp.org/HOWTO/Multicast-HOWTO-6.html
Status: Open
Priority: Medium. All standards compatibility is important to NuttX. However, most
the mechanism for leaving and joining groups is hidden behind a wrapper
function so that little of this incompatibilities need be exposed.
```

Start by reviewing NuttX's existing ioctl-based wrapper for joining and leaving IGMP multicast groups, including its device-name lookup. Compare it with the Linux setsockopt() IP_ADD_MEMBERSHIP and IP_DROP_MEMBERSHIP interface and the RFC3678 requirements. Done means providing standards-compatible group membership handling, including the stated IGMPv3 and IP-address lookup concerns.

Written by the indexing model from the issue text.