blockcheck: test tpws exists

blockcheck.sh

@@ -341,6 +341,12 @@ netcat_test()
 	}
 }
 
+tpws_can_fix_seg()
+{
+	# fix-seg requires kernel 4.6+
+	"$TPWS" --port 1 --dry-run --fix-seg >/dev/null 2>/dev/null
+}
+
 check_system()
 {
 	echo \* checking system
@@ -355,7 +361,14 @@ check_system()
 		Linux)
 			PKTWS="$NFQWS"
 			PKTWSD=nfqws
-			FIX_SEG='--fix-seg'
+			if [ -x "$TPWS" ] ; then
+				if tpws_can_fix_seg ; then
+					echo tpws supports --fix-seg on this system
+					FIX_SEG='--fix-seg'
+				else
+					echo tpws does not support --fix-seg on this system
+				fi
+			fi
 			linux_fwtype
 			[ "$FWTYPE" = iptables -o "$FWTYPE" = nftables ] || {
 				echo firewall type $FWTYPE not supported in $UNAME