syscall: remove cloexecSocket fallback path

Support for Linux kernel versions requiring the fallback to CloseOnExec
was dropped from recent Go versions. The minimum Linux kernel version is
2.6.32 as of Go 1.18. The SOCK_CLOEXEC flag for the socket syscall is
supported since kernel version 2.6.27.

Follows a similar change for net.sysSocket in CL 403634.

For #45964

Change-Id: I8b6311f07c4ed7900a9af3ecb2e146c49db08665
Reviewed-on: https://go-review.googlesource.com/c/go/+/422374
Reviewed-by: Joedian Reid <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>
Auto-Submit: Tobias Klauser <[email protected]>
Reviewed-by: Ian Lance Taylor <[email protected]>
Run-TryBot: Tobias Klauser <[email protected]>

Author: tklauser

src/syscall/lsf_linux.go

@@ -48,7 +48,7 @@ type iflags struct {
 
 // Deprecated: Use golang.org/x/net/bpf instead.
 func SetLsfPromisc(name string, m bool) error {
-	s, e := cloexecSocket(AF_INET, SOCK_DGRAM, 0)
+	s, e := Socket(AF_INET, SOCK_DGRAM|SOCK_CLOEXEC, 0)
 	if e != nil {
 		return e
 	}

src/syscall/netlink_linux.go

@@ -50,7 +50,7 @@ func newNetlinkRouteRequest(proto, seq, family int) []byte {
 // NetlinkRIB returns routing information base, as known as RIB, which
 // consists of network facility information, states and parameters.
 func NetlinkRIB(proto, family int) ([]byte, error) {
-	s, err := cloexecSocket(AF_NETLINK, SOCK_RAW, NETLINK_ROUTE)
+	s, err := Socket(AF_NETLINK, SOCK_RAW|SOCK_CLOEXEC, NETLINK_ROUTE)
 	if err != nil {
 		return nil, err
 	}