commands: don't register min_alloc/max_alloc for the generic socket category

SocketManager throws internal_error for category_generic, aborting rtorrent over RPC.

test/src/test_command_local.h

@@ -0,0 +1,15 @@
+#include "test/helpers/test_fixture.h"
+
+class TestCommandLocal : public test_fixture {
+  CPPUNIT_TEST_SUITE(TestCommandLocal);
+
+  CPPUNIT_TEST(test_socket_category_commands);
+
+  CPPUNIT_TEST_SUITE_END();
+
+public:
+  void setUp();
+  void tearDown();
+
+  void test_socket_category_commands();
+};