update to termshark-2.4.0

while there, clean the go cache after removing the problematic source
file which seems to be needed with go 1.19, diff for this from jsing@

net/termshark/Makefile

@@ -3,7 +3,7 @@ BROKEN-arm64=	system/dumpcapext_arm64.go:25:6: DumpcapExt redeclared in this blo
 COMMENT=	terminal UI for tshark, inspired by Wireshark
 
 MODGO_MODNAME=	github.com/gcla/termshark/v2
-MODGO_VERSION=	v2.3.0
+MODGO_VERSION=	v2.4.0
 
 DISTNAME=	termshark-${MODGO_VERSION}
 
@@ -22,7 +22,8 @@ RUN_DEPENDS=	net/wireshark,-text
 # *shrug* builds ok with "go get" but ports build picks up something broken
 do-build:
 	-cd ${WRKSRC} && ${MODGO_BUILD_CMD} ${ALL_TARGET}/cmd/...
-	rm -f ${WRKDIR}/go/pkg/mod/github.com/gcla/term@v0.0.0-20191015020247-31cba2f9f402/termios/pty_openbsd.go
+	rm -f ${WRKDIR}/go/pkg/mod/github.com/gcla/term@*/termios/pty_openbsd.go
+	GOCACHE="${MODGO_GOCACHE}" go clean -cache
 	cd ${WRKSRC} && ${MODGO_BUILD_CMD} ${ALL_TARGET}/cmd/...
 
 .include "modules.inc"