unix: add POLLRDHUP to FreeBSD

POLLRDHUP is a poll(2) event applicable to stream sockets that notifies
when a remote peer closes a connection.

Change-Id: I03a192426f89bbd08fb27dda2716ffb888043c92
Reviewed-on: https://go-review.googlesource.com/c/sys/+/607797
Auto-Submit: Ian Lance Taylor <iant@google.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

unix/types_freebsd.go

@@ -356,6 +356,7 @@ const (
 	POLLRDNORM   = C.POLLRDNORM
 	POLLWRBAND   = C.POLLWRBAND
 	POLLWRNORM   = C.POLLWRNORM
+	POLLRDHUP    = C.POLLRDHUP
 )
 
 // Capabilities

unix/ztypes_freebsd_386.go

@@ -625,6 +625,7 @@ const (
 	POLLRDNORM   = 0x40
 	POLLWRBAND   = 0x100
 	POLLWRNORM   = 0x4
+	POLLRDHUP    = 0x4000
 )
 
 type CapRights struct {

unix/ztypes_freebsd_amd64.go

@@ -630,6 +630,7 @@ const (
 	POLLRDNORM   = 0x40
 	POLLWRBAND   = 0x100
 	POLLWRNORM   = 0x4
+	POLLRDHUP    = 0x4000
 )
 
 type CapRights struct {

unix/ztypes_freebsd_arm.go

@@ -616,6 +616,7 @@ const (
 	POLLRDNORM   = 0x40
 	POLLWRBAND   = 0x100
 	POLLWRNORM   = 0x4
+	POLLRDHUP    = 0x4000
 )
 
 type CapRights struct {

unix/ztypes_freebsd_arm64.go

@@ -610,6 +610,7 @@ const (
 	POLLRDNORM   = 0x40
 	POLLWRBAND   = 0x100
 	POLLWRNORM   = 0x4
+	POLLRDHUP    = 0x4000
 )
 
 type CapRights struct {

unix/ztypes_freebsd_riscv64.go

@@ -612,6 +612,7 @@ const (
 	POLLRDNORM   = 0x40
 	POLLWRBAND   = 0x100
 	POLLWRNORM   = 0x4
+	POLLRDHUP    = 0x4000
 )
 
 type CapRights struct {