epair: unbind prior to returning to userspace

If 'options RSS' is set we bind the epair tasks to different CPUs. We
must take care to not keep the current thread bound to the last CPU when
we return to userspace.

MFC after:	1 week
Sponsored by:	Orange Business Services

sys/net/if_epair.c

@@ -826,6 +826,9 @@ epair_mod_init(void)
 
 		epair_tasks.tasks++;
 	}
+	thread_lock(curthread);
+	sched_unbind(curthread);
+	thread_unlock(curthread);
 #else
 	snprintf(name, sizeof(name), "epair_task");