BUG/MAJOR: sample: Wrong stick-table name parsing in "if/unless" ACL condition.

BUG/MAJOR: sample: Wrong stick-table name parsing in "if/unless" ACL condition.

This bug was introduced by 1b8e68e commit which supposed the stick-table was always
stored in struct arg at parsing time. This is never the case with the usage of
"if/unless" conditions in stick-table declared as backends. In this case, this is
the name of the proxy which must be considered as the stick-table name.

This must be backported to 2.0.