r357614 added CTLFLAG_NEEDGIANT to make it easier to find nodes that are still not MPSAFE (or already are but aren’t properly marked). Use it in preparation for a general review of all nodes.
This is non-functional change that adds annotations to SYSCTL_NODE and SYSCTL_PROC nodes using one of the soon-to-be-required flags.
Mark obvious cases as MPSAFE.
All entries that haven't been marked as MPSAFE before are by default marked as NEEDGIANT.