[9.20] fix: test: Ignore ISC_R_CONNECTIONRESET in the TCP tests
requested to merge backport-4849-dispatch_test-fails-in-connected_shutdown-on-freebsd-9.20 into bind-9.20
On FreeBSD, the TCP connection callback could spuriously receive ISC_R_CONNECTIONRESET even when connection to the loopback interface. Skip the other checks in such case and graciously shutdown the TCP connection.
Closes #4849 (closed)
Backport of MR !9303 (merged)