media: look up BAP transports by their associated stream

media: look up BAP transports by their associated stream

To look up transports, use BAP stream pointers associated with them, not
the path strings stored in the stream user data. This makes it clearer
that transports presented to the sound server correspond to the actual
streams.  The Acquire/etc. of BAP transports are already tied to the
associated stream.

This fixes use-after-free crashes in pac_clear.  They occur because the
lifetime of the path string was either that of media transport or media
endpoint, which may be shorter than that of the BAP stream.  In such
case, pac_clear is entered with invalid pointer in stream user data,
leading to crash.  There are a few code paths for this, e.g. making
sound server delay its SetConfiguration response (e.g. gdb breakpoint)
to get dbus timeout, then disconnecting:

ERROR: AddressSanitizer: heap-use-after-free on address XXXX
READ of size 3 at 0x606000031640 thread T0
...
    #4 0x559891 in btd_debug src/log.c:117
    #5 0x46abfd in pac_clear profiles/audio/media.c:1096
    #6 0x79fcaf in bap_stream_clear_cfm src/shared/bap.c:914
    #7 0x7a060d in bap_stream_detach src/shared/bap.c:987
    #8 0x7a25ea in bap_stream_state_changed src/shared/bap.c:1210
    #9 0x7a29cd in stream_set_state src/shared/bap.c:1254
    #10 0x7be824 in stream_foreach_detach src/shared/bap.c:3820
    #11 0x71d15d in queue_foreach src/shared/queue.c:207
    #12 0x7beb98 in bt_bap_detach src/shared/bap.c:3836
    #13 0x5228cb in bap_disconnect profiles/audio/bap.c:1342
    #14 0x63247c in btd_service_disconnect src/service.c:305
freed by thread T0 here:
    #0 0x7f16708b9388 in __interceptor_free.part.0 (/lib64/libasan.so.8+0xb9388)
    #1 0x7f167071b8cc in g_free (/lib64/libglib-2.0.so.0+0x5b8cc)
    #2 0x7047b7 in remove_interface gdbus/object.c:660
    #3 0x70aef6 in g_dbus_unregister_interface gdbus/object.c:1394
    #4 0x47be30 in media_transport_destroy profiles/audio/transport.c:217
    #5 0x464ab9 in endpoint_remove_transport profiles/audio/media.c:270
    #6 0x464d26 in clear_configuration profiles/audio/media.c:292
    #7 0x464e69 in clear_endpoint profiles/audio/media.c:300
    #8 0x46516e in endpoint_reply profiles/audio/media.c:325
...

Fixes: 7b1b1a499cf3 ("media: clear the right transport when clearing BAP endpoint")