BUG/MINOR: session: Eval L4/L5 rules defined in the default section

BUG/MINOR: session: Eval L4/L5 rules defined in the default section

It is possible to define TCP/HTTP rules in a named default section to
inherit from it in a proxy. However, there is an issue with L4/L5 rules.
Only the lists of the current frontend are checked to know if an eval must
be performed. Nothing is done for an empty list. Of course, the lists of the
default proxy must also be checked to be sure to not ignored default L4/L5
rules. It is now fixed.

This patch should fix the issue #2637. It must be backported as far as 2.6.