CLEANUP: config: make the cfg_keyword parsers take a const for the defproxy

The default proxy was passed as a variable to all parsers instead of a
const, which is not without risk, especially when some timeout parsers used
to make some int pointers point to the default values for comparisons. We
want to be certain that none of these parsers will modify the defaults
sections by accident, so it's important to mark this proxy as const.

This patch touches all occurrences found (89).
diff --git a/src/da.c b/src/da.c
index c11e076..4189092 100644
--- a/src/da.c
+++ b/src/da.c
@@ -35,7 +35,7 @@
 };
 
 static int da_json_file(char **args, int section_type, struct proxy *curpx,
-                        struct proxy *defpx, const char *file, int line,
+                        const struct proxy *defpx, const char *file, int line,
                         char **err)
 {
 	if (*(args[1]) == 0) {
@@ -47,7 +47,7 @@
 }
 
 static int da_log_level(char **args, int section_type, struct proxy *curpx,
-                        struct proxy *defpx, const char *file, int line,
+                        const struct proxy *defpx, const char *file, int line,
                         char **err)
 {
 	int loglevel;
@@ -67,7 +67,7 @@
 }
 
 static int da_property_separator(char **args, int section_type, struct proxy *curpx,
-                                 struct proxy *defpx, const char *file, int line,
+                                 const struct proxy *defpx, const char *file, int line,
                                  char **err)
 {
 	if (*(args[1]) == 0) {
@@ -79,7 +79,7 @@
 }
 
 static int da_properties_cookie(char **args, int section_type, struct proxy *curpx,
-                          struct proxy *defpx, const char *file, int line,
+                          const struct proxy *defpx, const char *file, int line,
                           char **err)
 {
 	if (*(args[1]) == 0) {