zstream: force-install zstreamdump link

Accidentally introduced by commit dd00925.

Force-install the zstreamdump link, this is a supported configuration
and the install should not fail if it needs to overwrite an existing
file.

Also cd to work around some funny platforms as noted in AC_PROG_LN_S doc

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Ryan Moeller <ryan@iXsystems.com>
Reviewed-by: Allan Jude <allan@klarasystems.com>
Signed-off-by: Ahelenia Ziemiańska <nabijaczleweli@nabijaczleweli.xyz>
Closes openzfs#12143

cmd/zstream/Makefile.am

@@ -17,4 +17,4 @@ zstream_LDADD = \
 include $(top_srcdir)/config/CppCheck.am
 
 install-exec-hook:
-	$(LN_S) zstream $(DESTDIR)$(sbindir)/zstreamdump
+	cd $(DESTDIR)$(sbindir) && $(LN_S) -f zstream zstreamdump