tools/l2cap-tester: Fix memory leak

tools/l2cap-tester: Fix memory leak

Set close_on_unref on new created GIOChannel and don't close
its file descriptor.

126 (120 direct, 6 indirect) bytes in 1 blocks aredefinitely
	lost in loss record 24 of 28
at 0x4A06409: malloc (in/usr/lib64/valgrind/vgpreload_memcheck
	-amd64-linux.so)
by 0x3C9564D88E: g_malloc (in /usr/lib64/libglib-2.0.so.0.3600.3)
by 0x3C956881F4: g_io_channel_unix_new (in/usr/lib64/libglib-
	2.0.so.0.3600.3)
by 0x402A5A: l2cap_listen_cb (l2cap-tester.c:774)
by 0x3C95647DF5: g_main_context_dispatch (in/usr/lib64/
	libglib-2.0.so.0.3600.3)
by 0x3C95648147: ??? (in /usr/lib64/libglib-2.0.so.0.3600.3)
by 0x3C95648549: g_main_loop_run
	(in/usr/lib64/libglib-2.0.so.0.3600.3)
by 0x40A67C: tester_run (tester.c:784)
by 0x4026A9: main (l2cap-tester.c:991)