The implementations of var_tcp6() and var_udp6() on FreeBSD don't work
and fail to compile. var_tcp6() also makes uses of kmem access, which
I'm trying to disable in snmpd. Provide a patch to fix these problems.
Submitted upstream here: https://sourceforge.net/p/net-snmp/mailman/net-snmp-coders/thread/ZjEwNV5BiTOQ-Adi%40nuc/#msg58766857
Readd mibII/ipv6 since it now compiles and works in my manual testing.
Also, simply remove the IPV6 option. It has no effect, as --enable-ipv6
is the default.