OFStateManager: miscellaneous flowtable cleanup
OFStateManager: smash together flowtable headers/code

ft_utils.h is largely moved to ft.c.
OFStateManager: rearrange flowtable code/header

I moved the comments for non-static functions to the header file, and
rearranged the order of function definitions to match the header.
OFStateManager: remove FT_ASSERT

FT_NO_ERROR_CHECKING will never be defined, so no reason for this macro.
OFStateManager: remove ft_flow_modify_cookie

I did not find any message in the OpenFlow 1.3 spec that could modify a cookie.
OFStateManager: rename flowtable functions

ft_hash_create -> ft_create
ft_hash_delete -> ft_destroy
ft_hash_flow_add -> ft_add
ft_hash_flow_delete -> ft_delete
ft_hash_flow_delete_id -> ft_delete_id
ft_flow_first_match -> ft_first_match
ft_flow_query -> ft_query
ft_id_lookup -> ft_lookup
ft_flow_meta_match -> ft_entry_meta_match
ft_flow_mark_deleted -> ft_entry_mark_deleted
ft_flow_modify_effects -> ft_entry_modify_effects
ft_flow_clear_counters -> ft_entry_clear_counters
ft_flow_set_effects -> ft_entry_set_effects
entry_has_out_port -> ft_entry_has_out_port
prio_to_bucket_index -> ft_prio_to_bucket_index
match_to_bucket_index -> ft_match_to_bucket_index
flow_id_to_bucket_index -> ft_flow_id_to_bucket_index
OFStateManager: remove flowtable interface macros