Change RACK dependency on TCPHPTS from a build-time dependency to a load-

time dependency.

At present, RACK requires the TCPHPTS option to run. However, because
modules can be moved from machine to machine, this dependency is really
best assessed at load time rather than at build time.

Reviewed by:	rrs
Sponsored by:	Netflix
Differential Revision:	https://reviews.freebsd.org/D15756

sys/netinet/tcp_hpts.c

@@ -1960,3 +1960,4 @@ tcp_init_hptsi(void *st)
 }
 
 SYSINIT(tcphptsi, SI_SUB_KTHREAD_IDLE, SI_ORDER_ANY, tcp_init_hptsi, NULL);
+MODULE_VERSION(tcphpts, 1);

sys/netinet/tcp_stacks/rack.c

@@ -127,10 +127,6 @@ uma_zone_t rack_pcb_zone;
 struct sysctl_ctx_list rack_sysctl_ctx;
 struct sysctl_oid *rack_sysctl_root;
 
-#ifndef TCPHPTS
-fatal error missing option TCPHSTS in the build;
-#endif
-
 #define CUM_ACKED 1
 #define SACKED 2
 
@@ -9162,3 +9158,4 @@ static moduledata_t tcp_rack = {
 
 MODULE_VERSION(MODNAME, 1);
 DECLARE_MODULE(MODNAME, tcp_rack, SI_SUB_PROTO_DOMAIN, SI_ORDER_ANY);
+MODULE_DEPEND(MODNAME, tcphpts, 1, 1, 1);