MINOR: tcp-act: Rename "set-{mark,tos}" to "set-fc-{mark,tos}"

MINOR: tcp-act: Rename "set-{mark,tos}" to "set-fc-{mark,tos}"

"set-mark" and "set-tos" only alter packets from haproxy to client
(frontend connection). Since we may add support for equivalent keywords
on server side, we rename them with an explicit name to prevent
confusions.

Thus, we rename:
 - "set-mark" to "set-fc-mark"
 - "set-tos" to "set-fc-tos"

"set-mark" and "set-tos" were kept as aliases (to "set-fc-mark" and
"set-fc-tos" respectively) for now to prevent config breakage, but they
have been marked as deprecated so they can be removed in future version.