p2p: improve checkaddrman logging with duration in milliseconds

and update the function name to CheckAddrman (drop "Force") for
nicer log output as it is prefixed to each of these log messages:

2021-09-21T18:42:50Z [opencon] CheckAddrman: new 64864, tried 1690, total 66554 started
2021-09-21T18:42:50Z [opencon] CheckAddrman: completed (76.21ms)

The existing Doxygen documentation on the function already makes
clear that it is unaffected by m_consistency_check_ratio.

test/functional/feature_asmap.py

@@ -89,8 +89,8 @@ class AsmapTest(BitcoinTestFramework):
         self.restart_node(0, ["-asmap", "-checkaddrman=1"])
         with self.node.assert_debug_log(
             expected_msgs=[
-                "Addrman checks started: new 1, tried 1, total 2",
-                "Addrman checks completed successfully",
+                "CheckAddrman: new 1, tried 1, total 2 started",
+                "CheckAddrman: completed",
             ]
         ):
             self.node.getnodeaddresses()  # getnodeaddresses re-runs the addrman checks