cc_init() should only be run once on system boot, but with VIMAGE kernels it

runs on boot and each time a vnet jail is created. Running cc_init() multiple
times results in a panic when attempting to initialise the cc_list lock again,
and so r215166 effectively broke the use of vnet jails.

Switch to using a SYSINIT to run cc_init() on boot. CC algorithm modules loaded
on boot register in the same SI_SUB_PROTO_IFATTACHDOMAIN category as is used in
this patch, so cc_init() is run at SI_ORDER_FIRST to ensure the framework is
initialised before module registration is attempted.

Sponsored by:	FreeBSD Foundation
Reported and tested by:	Mikolaj Golub <to.my.trociny at gmail com>
MFC after:	11 weeks
X-MFC with:	r215166

sys/netinet/cc.h

@@ -62,7 +62,6 @@ extern struct cc_algo newreno_cc_algo;
 SYSCTL_DECL(_net_inet_tcp_cc);
 
 /* CC housekeeping functions. */
-void	cc_init(void);
 int	cc_register_algo(struct cc_algo *add_cc);
 int	cc_deregister_algo(struct cc_algo *remove_cc);
 

sys/netinet/cc/cc.c

@@ -176,8 +176,8 @@ cc_list_available(SYSCTL_HANDLER_ARGS)
 /*
  * Initialise CC subsystem on system boot.
  */
-void
-cc_init()
+static void
+cc_init(void)
 {
 	CC_LIST_LOCK_INIT();
 	STAILQ_INIT(&cc_list);
@@ -328,6 +328,8 @@ cc_modevent(module_t mod, int event_type, void *data)
 	return (err);
 }
 
+SYSINIT(cc, SI_SUB_PROTO_IFATTACHDOMAIN, SI_ORDER_FIRST, cc_init, NULL);
+
 /* Declare sysctl tree and populate it. */
 SYSCTL_NODE(_net_inet_tcp, OID_AUTO, cc, CTLFLAG_RW, NULL,
     "congestion control related settings");

sys/netinet/tcp_subr.c

@@ -278,8 +278,6 @@ tcp_init(void)
 {
 	int hashsize;
 
-	cc_init();
-
 	hashsize = TCBHASHSIZE;
 	TUNABLE_INT_FETCH("net.inet.tcp.tcbhashsize", &hashsize);
 	if (!powerof2(hashsize)) {