Fix docstring in method list_routers_on_l3_agent
Fix docstring in method list_routers_on_l3_agent

For function list_routers_on_l3_agent in the
python-neutronclient\neutronclient\v2_0\client.py,
the description is "Fetches a list of L3 agents
hosting a router". However this function fetches
a list of routers hosted on a L3 agent.

Change the docstring.

Change-Id: Ia2156b5f6f016f338549a6536a0f31bf9e96c7cf
Closes-Bug: 1802475

openstack/python-neutronclient,noironetworks/python-neutronclient,noironetworks/python-neutronclient,openstack/python-neutronclient