BUG/MINOR: config: Properly test warnif_misplaced_* return values

BUG/MINOR: config: Properly test warnif_misplaced_* return values

warnif_misplaced_* functions return 1 when a warning is reported and 0
otherwise. So the caller must properly handle the return value.

When parsing a proxy, ERR_WARN code must be added to the error code instead
of the return value. When a warning was reported, ERR_RETRYABLE (1) was
added instead of ERR_WARN.

And when tcp rules were parsed, warnings were ignored. Message were emitted
but the return values were ignored.

This patch should be backported to all stable versions.