syscall: drop fallback to accept in Accept on Linux

The minimum required Linux kernel version for Go 1.18 will be changed to
2.6.32, see #45964. The current minimum required version is 2.6.23 and
accept4 was added in 2.6.28, so the fallback to accept in Accept on
Linux can be removed.

For #45964

Change-Id: I78fc4e5b58417bbc540912c9dbf1b1b3db888fea
Reviewed-on: https://go-review.googlesource.com/c/go/+/346849
Trust: Tobias Klauser <[email protected]>
Run-TryBot: Tobias Klauser <[email protected]>
TryBot-Result: Go Bot <[email protected]>
Reviewed-by: Brad Fitzpatrick <[email protected]>

Author: tklauser

src/syscall/syscall_linux.go

@@ -542,11 +542,7 @@ func anyToSockaddr(rsa *RawSockaddrAny) (Sockaddr, error) {
 func Accept(fd int) (nfd int, sa Sockaddr, err error) {
 	var rsa RawSockaddrAny
 	var len _Socklen = SizeofSockaddrAny
-	// Try accept4 first for Android, then try accept for kernel older than 2.6.28
 	nfd, err = accept4(fd, &rsa, &len, 0)
-	if err == ENOSYS {
-		nfd, err = accept(fd, &rsa, &len)
-	}
 	if err != nil {
 		return
 	}