ip_mroute: Fix sysctl knobs

[zlei]

Summary

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

Test Plan

Load module ip_mroute and check SYSCTLs.

# kenv net.inet.ip.mfchashsize=512
net.inet.ip.mfchashsize="512"
# kenv net.inet.pim.squelch_wholepkt=1
net.inet.pim.squelch_wholepkt="1"
# kldload ip_mroute
# sysctl -T net.inet.ip.mfchashsize
net.inet.ip.mfchashsize: 512
# sysctl -T net.inet.pim.squelch_wholepkt
net.inet.pim.squelch_wholepkt: 1

Note:

• net.inet.ip.mfchashsize default is 256 (MFCHASHSIZE)
• net.inet.pim.squelch_wholepkt default is 0