BUG/MINOR: sink: don't learn srv port from srv addr

Since 04276f3d ("MEDIUM: server: split the address and the port into two
different fields") we should not use srv->addr to store server's port
and rely on srv->svc_port instead.

For sink servers, we correctly set >svc_port upon server creation but
we didn't use it when initializing address for the connection.

As a result, FQDN resolution will not work properly with sink servers.
Hopefully, this used to work by accident because sink servers were
resolved using the PA_O_RESOLVE flag in str2sa_range(), which made the
srv->addr contain the port in addition to the address.

But this will fail to work when FQDN resolution is postponed because only
->svc_port will contain the proper server port upon resolution.

For instance, FQDN resolution with servers from log backends (which are
resolved as regular servers, that is, without the PA_O_RESOLVE) will fail
to work because of this.

This may be backported as far as 2.2 even though the bug didn't have
noticeable effects for versions below 2.9

[In 2.2, sink_forward_session_init() didn't exist it should be applied in
 sink_forward_session_create()]

src/sink.c

@@ -577,6 +577,8 @@ static int sink_forward_session_init(struct appctx *appctx)
 
 	if (!sockaddr_alloc(&addr, &sft->srv->addr, sizeof(sft->srv->addr)))
 		goto out_error;
+	/* srv port should be learned from srv->svc_port not from srv->addr */
+	set_host_port(addr, sft->srv->svc_port);
 
 	if (appctx_finalize_startup(appctx, sft->srv->proxy, &BUF_NULL) == -1)
 		goto out_free_addr;