um: vector: Reduce stack usage in vector_eth_configure()

When compiling with clang (19.1.7), initializing *vp using a compound
literal may result in excessive stack usage. Fix it by initializing the
required fields of *vp individually.

Without this patch:

$ objdump -d arch/um/drivers/vector_kern.o | ./scripts/checkstack.pl x86_64 0
...
0x0000000000000540 vector_eth_configure [vector_kern.o]:1472
...

With this patch:

$ objdump -d arch/um/drivers/vector_kern.o | ./scripts/checkstack.pl x86_64 0
...
0x0000000000000540 vector_eth_configure [vector_kern.o]:208
...

Reported-by: kernel test robot <[email protected]>
Closes: https://lore.kernel.org/oe-kbuild-all/[email protected]/
Signed-off-by: Tiwei Bie <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Johannes Berg <[email protected]>

Author: btw616

arch/um/drivers/vector_kern.c

@@ -1625,35 +1625,19 @@ static void vector_eth_configure(
 
 	device->dev = dev;
 
-	*vp = ((struct vector_private)
-		{
-		.list			= LIST_HEAD_INIT(vp->list),
-		.dev			= dev,
-		.unit			= n,
-		.options		= get_transport_options(def),
-		.rx_irq			= 0,
-		.tx_irq			= 0,
-		.parsed			= def,
-		.max_packet		= get_mtu(def) + ETH_HEADER_OTHER,
-		/* TODO - we need to calculate headroom so that ip header
-		 * is 16 byte aligned all the time
-		 */
-		.headroom		= get_headroom(def),
-		.form_header		= NULL,
-		.verify_header		= NULL,
-		.header_rxbuffer	= NULL,
-		.header_txbuffer	= NULL,
-		.header_size		= 0,
-		.rx_header_size		= 0,
-		.rexmit_scheduled	= false,
-		.opened			= false,
-		.transport_data		= NULL,
-		.in_write_poll		= false,
-		.coalesce		= 2,
-		.req_size		= get_req_size(def),
-		.in_error		= false,
-		.bpf			= NULL
-	});
+	INIT_LIST_HEAD(&vp->list);
+	vp->dev		= dev;
+	vp->unit	= n;
+	vp->options	= get_transport_options(def);
+	vp->parsed	= def;
+	vp->max_packet	= get_mtu(def) + ETH_HEADER_OTHER;
+	/*
+	 * TODO - we need to calculate headroom so that ip header
+	 * is 16 byte aligned all the time
+	 */
+	vp->headroom	= get_headroom(def);
+	vp->coalesce	= 2;
+	vp->req_size	= get_req_size(def);
 
 	dev->features = dev->hw_features = (NETIF_F_SG | NETIF_F_FRAGLIST);
 	INIT_WORK(&vp->reset_tx, vector_reset_tx);