devel/py-usbtmc: Disable kernel driver detaching

The original code uses the "kernel driver detach" functionality
which is required under Linux but not available under FreeBSD.

devel/py-usbtmc/Makefile

@@ -1,6 +1,7 @@
 PORTNAME=	usbtmc
 DISTVERSIONPREFIX=	v
 DISTVERSION=	0.8
+PORTREVISION=	1
 CATEGORIES=	devel python
 PKGNAMEPREFIX=	${PYTHON_PKGNAMEPREFIX}
 

devel/py-usbtmc/files/patch-usbtmc.py

@@ -0,0 +1,11 @@
+--- usbtmc/usbtmc.py.orig	2017-01-18 05:35:14 UTC
++++ usbtmc/usbtmc.py
+@@ -841,7 +841,7 @@
+             raise NotImplementedError()
+ 
+     def _release_kernel_driver(self, interface_number):
+-        if os.name == 'posix':
++        if os.name == 'posix' and os.uname()[0] != 'FreeBSD':
+             if self.device.is_kernel_driver_active(interface_number):
+                 self.reattach.append(interface_number)
+                 try: