dpctl: Support flush conntrack by conntrack 5-tuple

dpctl: Support flush conntrack by conntrack 5-tuple

With this patch, "flush-conntrack" in ovs-dpctl and ovs-appctl accept
a conntrack 5-tuple to delete the conntrack entry specified by the 5-tuple.
For example, user can use the following command to flush a conntrack entry
in zone 5.

$ ovs-dpctl flush-conntrack zone=5 \
  'ct_nw_src=10.1.1.2,ct_nw_dst=10.1.1.1,ct_nw_proto=17,ct_tp_src=2,ct_tp_dst=1'

$ ovs-appctl dpctl/flush-conntrack zone=5 \
  'ct_nw_src=10.1.1.2,ct_nw_dst=10.1.1.1,ct_nw_proto=17,ct_tp_src=2,ct_tp_dst=1'

VMWare-BZ: #1983178
Signed-off-by: Yi-Hung Wei <yihung.wei@gmail.com>
Signed-off-by: Justin Pettit <jpettit@ovn.org>