feat: get_management_peer, the address the host sees the SSH connection come from

From SSH_CONNECTION's client side; None when it is empty or no address.
The caller uses it to choose the sources an SNMP agent answers.

tests/test_fix_templates.py

@@ -191,3 +191,23 @@ def test_every_annotation_resolves():
     for name, member in inspect.getmembers(LinuxDriver, inspect.isfunction):
         if member.__module__ == "napalm_linux.linux":
             typing.get_type_hints(member)
+
+
+class TestManagementPeer:
+    """The address the host sees this connection come from (``SSH_CONNECTION``)."""
+
+    def _driver(self, answer):
+        d = LinuxDriver("h", "admin", "p")
+        d._device = MagicMock()
+        d.run_command = MagicMock(return_value=MagicMock(stdout=answer, exit_code=0))
+        return d
+
+    def test_the_client_side_of_ssh_connection(self):
+        assert self._driver("10.7.224.20 51234 10.0.0.5 22\n").get_management_peer() == "10.7.224.20"
+
+    def test_an_ipv6_client(self):
+        assert self._driver("fd00::20 51234 fd00::5 22\n").get_management_peer() == "fd00::20"
+
+    @pytest.mark.parametrize("answer", ["", "\n", "garbage", "not-an-ip 1 2 3"])
+    def test_nothing_usable_is_none(self, answer):
+        assert self._driver(answer).get_management_peer() is None