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/types/stick_table.h b/include/types/stick_table.h
index 28e255f..695a75c 100644
--- a/include/types/stick_table.h
+++ b/include/types/stick_table.h
@@ -144,6 +144,13 @@
 /* stick table */
 struct stktable {
 	char *id;		  /* table id name */
+	struct stktable *next;    /* The stick-table may be linked when belonging to
+	                           * the same configuration section.
+	                           */
+	struct {
+		const char *file;     /* The file where the stick-table is declared. */
+		int line;             /* The line in this <file> the stick-table is declared. */
+	} conf;
 	struct eb_root keys;      /* head of sticky session tree */
 	struct eb_root exps;      /* head of sticky session expiration tree */
 	struct eb_root updates;   /* head of sticky updates sequence tree */
@@ -175,6 +182,7 @@
 		unsigned int u;
 		void *p;
 	} data_arg[STKTABLE_DATA_TYPES]; /* optional argument of each data type */
+	struct proxy *proxy;      /* The proxy this stick-table is attached to, if any.*/
 };
 
 extern struct stktable_data_type stktable_data_types[STKTABLE_DATA_TYPES];