Build break: ADD_FILTER references undefined EVL_VLID_MASK macro — dead code not in any build

Summary

ng_vlan.c:218 validates vlan id with if(vf->vlan & ~EVL_VLID_MASK) but EVL_VLID_MASK is NEVER defined anywhere in the entire tree (rg confirms single reference). Intended symbol is 0x0FFF 12-bit VID mask from older FreeBSD if_vlan_var.h dropped during VLAN rework. File is DEAD CODE: not in sys/conf/files not in sys/netgraph7/Makefile SUBDIR not in any sys/config/* kernel config. Would fail to compile if revived. If maintainer fixes build by deleting check instead of defining mask ADD_FILTER accepts arbitrary 16-bit vlan values stored in evl_tag but still hash-bounded (HASH &0x0f) so not memory-safety. No runtime impact today. Fix: define EVL_VLID_MASK in if_vlan_var.h or use existing EVL_VLANOFTAG(tag)((tag)&4095).