datapath: Eliminate 'flags' member from odp_flow.

datapath: Eliminate 'flags' member from odp_flow.

Nothing was productively using the 'flags' member of odp_flow, so this
commit removes it.

ODPFF_ZERO_TCP_FLAGS isn't used at all (as of the previous commit).

ODPFF_EOF has been replaced by a special case of the 'key_len' member.
This will go away, too, once AF_NETLINK starts being used.

Signed-off-by: Ben Pfaff <blp@nicira.com>
Acked-by: Jesse Gross <jesse@nicira.com>