MEDIUM: init: convert all trivial registration calls to initcalls

This switches explicit calls to various trivial registration methods for
keywords, muxes or protocols from constructors to INITCALL1 at stage
STG_REGISTER. All these calls have in common to consume a single pointer
and return void. Doing this removes 26 constructors. The following calls
were addressed :

- acl_register_keywords
- bind_register_keywords
- cfg_register_keywords
- cli_register_kw
- flt_register_keywords
- http_req_keywords_register
- http_res_keywords_register
- protocol_register
- register_mux_proto
- sample_register_convs
- sample_register_fetches
- srv_register_keywords
- tcp_req_conn_keywords_register
- tcp_req_cont_keywords_register
- tcp_req_sess_keywords_register
- tcp_res_cont_keywords_register
- flt_register_keywords
diff --git a/src/server.c b/src/server.c
index 0cf5eca..eb2bc6e 100644
--- a/src/server.c
+++ b/src/server.c
@@ -19,6 +19,7 @@
 #include <common/cfgparse.h>
 #include <common/config.h>
 #include <common/errors.h>
+#include <common/initcall.h>
 #include <common/namespace.h>
 #include <common/time.h>
 
@@ -1221,11 +1222,7 @@
 	{ NULL, NULL, 0 },
 }};
 
-__attribute__((constructor))
-static void __listener_init(void)
-{
-	srv_register_keywords(&srv_kws);
-}
+INITCALL1(STG_REGISTER, srv_register_keywords, &srv_kws);
 
 /* Recomputes the server's eweight based on its state, uweight, the current time,
  * and the proxy's algorihtm. To be used after updating sv->uweight. The warmup
@@ -4700,11 +4697,7 @@
 	{{},}
 }};
 
-__attribute__((constructor))
-static void __server_init(void)
-{
-	cli_register_kw(&cli_kws);
-}
+INITCALL1(STG_REGISTER, cli_register_kw, &cli_kws);
 
 /*
  * This function applies server's status changes, it is