Use the standard test/[ command.

We use it elsewhere; use it here, as FreeBSD's /bin/sh doesn't support
[[ as a test operator.

Change-Id: I183b10cc6f4aceec9725027474848061e8ea4fd9
Reviewed-on: https://code.wireshark.org/review/29232
Reviewed-by: Guy Harris <guy@alum.mit.edu>

tools/bsd-setup.sh

@@ -83,7 +83,7 @@ add_package() {
 	local list="$1" pkgname="$2"
 
 	# fail if the package is not known
-	if [[ "$PM_MUST_GLOB" == yes ]]
+	if [ "$PM_MUST_GLOB" = yes ]
 	then
 		#
 		# We need to do a glob search, with a "*" at the