Fix build: in a recent pf refactor (head@240233), pf_var.h was modified
to not include netinet/tcp_fsm.h, and HEAD tcpdump rely on this change
as the tcp_fsm.h will only be processed once.

Solve this by defining TCPSTATES earlier. This wouldn't cause breakage
should pf be merged in the future.

Noticed by: tinderbox via many
Pointy hat to: delphij