Lock down global variables in if_gre:

- Add gre_mtx to protect global softc list.
- Hold gre_mtx over various list operations (insert, delete).
- Centralize if_gre interface teardown in gre_destroy(), and call this
  from modevent unload and gre_clone_destroy().
- Export gre_mtx to ip_gre.c, which walks the gre list to look up gre
  interfaces during encapsulation.  Add a wonking comment on how we need
  some sort of drain/reference count mechanism to keep gre references
  alive while in use and simultaneous destroy.

This commit does not lockdown softc data, which follows in a future
commit.

0 files changed, 0 insertions, 0 deletions