The dup2 syscalls is not available on riscv64. However, using dup3 with
zero as a flags argument is equivalent.

diff -upr termshark-2.2.0.orig/system/dumpcapext.go termshark-2.2.0/system/dumpcapext.go
--- termshark-2.2.0.orig/system/dumpcapext.go	2021-07-10 16:53:56.607649135 +0200
+++ termshark-2.2.0/system/dumpcapext.go	2021-07-10 16:55:47.034414600 +0200
@@ -47,7 +47,7 @@ func DumpcapExt(dumpcapBin string, tshar
 				if err != nil {
 					log.Warnf("Unexpected error parsing %s: %v", args[1], err)
 				} else {
-					err = syscall.Dup2(fd, 0)
+					err = syscall.Dup3(fd, 0, 0)
 					if err != nil {
 						log.Warnf("Problem duplicating fd %d to 0: %v", fd, err)
 						log.Warnf("Will not try to replace argument %s to tshark", args[1])