Bump oslo.config to 2.5.0
Ryu is using item_type since commit so oslo.config minimum
version needs to be updated.
eventlet!=0.18.3,>=0.18.2,!=0.20.1,!=0.21.0,!=0.23.0
msgpack>=0.3.0 # RPC library, BGP speaker(net_cntl)
netaddr
-oslo.config>=1.15.0
+oslo.config>=2.5.0
ovs>=2.6.0 # OVSDB
routes # wsgi
six>=1.4.0
