caprevoke: Avoid validating CLGs if revocation is in progress

When forking, the GCLG and LCLGs may be out of sync if a new revocation epoch
was opened (bumping the GCLG) but the background scan has not yet started
(background scans block fork()).  This can arise if a cheri_revoke() is called
without either of the CHERI_REVOKE_LAST_PASS and CHERI_REVOKE_ASYNC flags.

sys/vm/vm_cheri_revoke.c

@@ -1120,6 +1120,8 @@ vm_cheri_assert_consistent_clg(struct vm_map *map)
 
 	if (!cheri_validate_clg)
 		return;
+	if (cheri_revoke_st_is_revoking(map->vm_cheri_revoke_st))
+		return;
 	VM_MAP_ENTRY_FOREACH(entry, map) {
 		if ((entry->max_protection & VM_PROT_READ_CAP) == 0)
 			continue;