This object indicates the IGMP packet forwarding mode.
Only the value transparent(1) is supported currently.
Options:
1. transparent(1) - Indicates that the IGMP upstream packets forward mode is transparent
2. translation(2) - Indicates that the IGMP upstream packets forward mode is translation
3. default(3) - Indicates that the IGMP upstream packets forward mode is add VLAN tag
4. invalid(-1) - Indicates that the query fails or no information is detected.