sbin/ifconfig: document new nwflag uapsd

OK: phessler@, stsp@

sbin/ifconfig/ifconfig.8

@@ -1,4 +1,4 @@
-.\"	$OpenBSD: ifconfig.8,v 1.413 2025/12/03 10:19:27 stsp Exp $
+.\"	$OpenBSD: ifconfig.8,v 1.414 2026/05/28 10:52:39 kirill Exp $
 .\"	$NetBSD: ifconfig.8,v 1.11 1996/01/04 21:27:29 pk Exp $
 .\"     $FreeBSD: ifconfig.8,v 1.16 1998/02/01 07:03:29 steve Exp $
 .\"
@@ -31,7 +31,7 @@
 .\"
 .\"     @(#)ifconfig.8	8.4 (Berkeley) 6/1/94
 .\"
-.Dd $Mdocdate: December 3 2025 $
+.Dd $Mdocdate: May 28 2026 $
 .Dt IFCONFIG 8
 .Os
 .Sh NAME
@@ -1111,6 +1111,14 @@ flag will disable MIMO reception and transmission even if the driver
 and wireless network device support MIMO.
 This flag can be used to work around packet loss in 11n mode if the
 wireless network device has unused antenna connectors.
+.It uapsd
+The
+.Ql uapsd
+flag will enable Unscheduled Automatic Power Save Delivery
+(u-APSD) support.
+This can reduce power consumption while the interface is idle or
+carrying little traffic, but may increase latency for sparse traffic.
+This flag is disabled by default.
 .It stayauth
 The
 .Ql stayauth