mcastmngr: Handled max multicast snoop entry
- removed +2 logic as multicast snoop entry handled in mcproxy with logic to exclude count of reserve mcast ip address subnet
- pipeline execution result https://dev.iopsys.eu/feed/iopsys/-/merge_requests/new?merge_request%5Bsource_branch%5D=mcproxy_max_snooping_entry
- related mcproxy MR link openwrt-routing!34 (merged)