tcp: fix build on riscv64 (#2590)

* tcp: fix build on riscv64

* explain why riscv64 doesn't work

Co-authored-by: Jorropo <jorropo.pgm@gmail.com>

---------

Co-authored-by: Jorropo <jorropo.pgm@gmail.com>

p2p/transport/tcp/metrics.go

@@ -1,4 +1,4 @@
-//go:build !windows
+//go:build !windows && !riscv64
 
 package tcp
 

p2p/transport/tcp/metrics_general.go

@@ -1,4 +1,4 @@
-//go:build !linux && !darwin && !windows
+//go:build !linux && !darwin && !windows && !riscv64
 
 package tcp
 

p2p/transport/tcp/metrics_windows.go → p2p/transport/tcp/metrics_none.go

@@ -1,4 +1,6 @@
-//go:build windows
+// riscv64 see: https://github.com/marten-seemann/tcp/pull/1
+
+//go:build windows || riscv64
 
 package tcp