Fix typo in openbsd build constraint (#125)

I noticed this when building termshark with Go 1.17.
diff --git a/ztypes_openbsd_32bit_int.go b/ztypes_openbsd_32bit_int.go
index dee9e62..c9aa316 100644
--- a/ztypes_openbsd_32bit_int.go
+++ b/ztypes_openbsd_32bit_int.go
@@ -1,4 +1,4 @@
-//go:build (386 || amd64 || arm || arm64 || mips64) && solaris
+//go:build (386 || amd64 || arm || arm64 || mips64) && openbsd
 //+build openbsd
 //+build 386 amd64 arm arm64 mips64