internal/envoy: hard code Linux system call constants

When programming the Envoy socket options, we need to use system call
constants for the platform that Envoy is running on. Ensure that we
always use Linux values since that is what we know (by fiat) that
Envoy is running on.

This fixes projectcontour#2729.

Signed-off-by: James Peach <jpeach@vmware.com>

internal/envoy/tcp_keepalive.go

@@ -24,6 +24,15 @@ const (
 	TCP_KEEPIDLE  = 0x4 // Linux syscall.TCP_KEEPIDLE
 	TCP_KEEPINTVL = 0x5 // Linux syscall.TCP_KEEPINTVL
 	TCP_KEEPCNT   = 0x6 // Linux syscall.TCP_KEEPCNT
+
+	// The following are Linux syscall constants for all
+	// architectures except MIPS.
+	SOL_SOCKET   = 0x1
+	SO_KEEPALIVE = 0x9
+
+	// IPPROTO_TCP has the same value across Go platforms, but
+	// is defined here for consistency.
+	IPPROTO_TCP = syscall.IPPROTO_TCP
 )
 
 func TCPKeepaliveSocketOptions() []*envoy_api_v2_core.SocketOption {
@@ -35,24 +44,24 @@ func TCPKeepaliveSocketOptions() []*envoy_api_v2_core.SocketOption {
 		// Enable TCP keep-alive.
 		{
 			Description: "Enable TCP keep-alive",
-			Level:       syscall.SOL_SOCKET,
-			Name:        syscall.SO_KEEPALIVE,
+			Level:       SOL_SOCKET,
+			Name:        SO_KEEPALIVE,
 			Value:       &envoy_api_v2_core.SocketOption_IntValue{IntValue: 1},
 			State:       envoy_api_v2_core.SocketOption_STATE_LISTENING,
 		},
 		// The time (in seconds) the connection needs to remain idle
 		// before TCP starts sending keepalive probes.
 		{
 			Description: "TCP keep-alive initial idle time",
-			Level:       syscall.IPPROTO_TCP,
+			Level:       IPPROTO_TCP,
 			Name:        TCP_KEEPIDLE,
 			Value:       &envoy_api_v2_core.SocketOption_IntValue{IntValue: 45},
 			State:       envoy_api_v2_core.SocketOption_STATE_LISTENING,
 		},
 		// The time (in seconds) between individual keepalive probes.
 		{
 			Description: "TCP keep-alive time between probes",
-			Level:       syscall.IPPROTO_TCP,
+			Level:       IPPROTO_TCP,
 			Name:        TCP_KEEPINTVL,
 			Value:       &envoy_api_v2_core.SocketOption_IntValue{IntValue: 5},
 			State:       envoy_api_v2_core.SocketOption_STATE_LISTENING,
@@ -62,7 +71,7 @@ func TCPKeepaliveSocketOptions() []*envoy_api_v2_core.SocketOption {
 		// obtained from the other end.
 		{
 			Description: "TCP keep-alive probe count",
-			Level:       syscall.IPPROTO_TCP,
+			Level:       IPPROTO_TCP,
 			Name:        TCP_KEEPCNT,
 			Value:       &envoy_api_v2_core.SocketOption_IntValue{IntValue: 9},
 			State:       envoy_api_v2_core.SocketOption_STATE_LISTENING,