tun: checksum tests and benchmarks

Signed-off-by: Adrian Dewhurst <[email protected]>

Author: sailorfrag

tun/checksum_generic_test.go

@@ -0,0 +1,9 @@
+package tun
+
+var archChecksumFuncs = []archChecksumDetails{
+	{
+		name:      "generic",
+		available: true,
+		f:         checksum,
+	},
+}