BUG/MINOR: config: correctly report when log-format headers require HTTP mode

When using some log-format directives in header insertion without HTTP mode,
the config parser used to report a cryptic message about option httplog being
downgraded to tcplog and with "(null):0" as the file name and line number.

This is because the lfs_file and lfs_line were not properly set for some valid
use cases of log-format directives. Now we cover http-request and http-response
as well.