MINOR: config: Extract the code of "stick-table" line parsing.

With this patch we move the code responsible of parsing "stick-table"
lines to implement parse_stick_table() function in src/stick-tabble.c
so that to be able to parse "stick-table" elsewhere than in proxy sections.
We have have also added a conf struct to stktable struct to store the filename
and the line in the file the stick-table has been parsed to help in
diagnosing and displaying any configuration issue.
diff --git a/include/proto/stick_table.h b/include/proto/stick_table.h
index 40bb8ca..962c95a 100644
--- a/include/proto/stick_table.h
+++ b/include/proto/stick_table.h
@@ -38,6 +38,8 @@
 
 int stktable_init(struct stktable *t);
 int stktable_parse_type(char **args, int *idx, unsigned long *type, size_t *key_size);
+int parse_stick_table(const char *file, int linenum, char **args,
+                      struct stktable *t, char *id, struct peers *peers);
 struct stksess *stktable_get_entry(struct stktable *table, struct stktable_key *key);
 struct stksess *stktable_set_entry(struct stktable *table, struct stksess *nts);
 void stktable_touch_with_exp(struct stktable *t, struct stksess *ts, int decrefcount, int expire);