The loader tunable net.inet.ip.mfchashsize does not have corresponding
sysctl MIB entry. Just add it.
While here, the sysctl variable net.inet.pim.squelch_wholepkt is actually
a loader tunable. Add sysctl flag CTLFLAG_TUN to it so that sysctl -T
can report it correctly.
Fixes: 443fc3176dee Introduce a number of changes to the MROUTING code
MFC after: 3 days