ofproto-dpif.at: Avoid using GNU sed extensions

Introduced by commit f9038ef61e0bf89bcd753b7cfd187adb112601ec.
("recirculation: Map recirc_id to ofproto_dpif.")

Signed-off-by: YAMAMOTO Takashi <yamamoto@valinux.co.jp>
Acked-by: Alex Wang <alexw@nicira.com>