Handle double timeout in udp_cancel_read test
If sending took too long the isc_nm_read() could timeout twice, leading to extra 'cread' counter in the udp_cancel_read test. Increase the cread counter only on ISC_R_EOF (canceled read) and deal with the multiple ISC_R_TIMEOUTS gracefully.
See #3595 (closed)
Edited by Michał Kępień