`in_getmulti` implicitly relies on the caller to add a reference when a new multicast address is created and *not* do so when it's an existing one. Breaking this contract has led to pf and carp causing use after free and could be causing in_multi leaks.
```
pkg install mdnsresponder
sysrc mdnsd_enable=YES
service mdnsd start
ifconfig vtnet0 delete # or whatever iface egress/dhclient is running on
ifconfig epair create
ifconfig epair0a 0/24 up
ifconfig epair0a destroy
# panic
```