in luci-app-dawn, if eval_probe_req is not ticked, eval_probe_req would be -1.
however, in c language, !(-1) is false.
Since only zero in if statement is false, non-zero number is true.
DAWN currently tries to update it's list of TCP socket endpoints using
mDNS when it is configured to use UDP.
Only update the TCP socket list when DAWN is configured to use TCP
sockets.
Fix a identation mismatch along the way.