tools: bpf_asm: cleanup vlan extension related token

We now have K_VLANT, K_VLANP and K_VLANTPID. Clean them up into more
descriptive token, namely K_VLAN_TCI, K_VLAN_AVAIL and K_VLAN_TPID.

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: David S. Miller <davem@davemloft.net>