vfio-user: fix VFIO_PROXY_USE_MULTI constant value

The constant value should represent the next bit in the VFIOProxy flags which
is 0x10 and not 0x16.

Signed-off-by: Mark Cave-Ayland <mark.caveayland@nutanix.com>
Fixes: 1a0c32a9da ("vfio-user: add coalesced posted writes")
Reviewed-by: John Levon <john.levon@nutanix.com>
Link: https://lore.kernel.org/qemu-devel/20260121110055.2333711-2-mark.caveayland@nutanix.com
Signed-off-by: Cédric Le Goater <clg@redhat.com>

hw/vfio-user/proxy.h

@@ -94,7 +94,7 @@ typedef struct VFIOUserProxy {
 #define VFIO_PROXY_CLIENT        0x1
 #define VFIO_PROXY_FORCE_QUEUED  0x4
 #define VFIO_PROXY_NO_POST       0x8
-#define VFIO_PROXY_USE_MULTI     0x16
+#define VFIO_PROXY_USE_MULTI     0x10
 
 /* coalescing high and low water marks for VFIOProxy num_outgoing */
 #define VFIO_USER_OUT_HIGH       1024