[pfcwd] Add half of polling time as compensation for test_pfcwd_timer_accuracy#14589

StormLiangMS merged 3 commits intosonic-net:mastersonic-net/sonic-mgmt:masterfrom

lipxu:20240914_publicMaster_pfcwd_pollinglipxu/sonic-mgmt-lipxu-fork:20240914_publicMaster_pfcwd_pollingCopy head branch name to clipboard