icera,hso: don't disconnect() cancellable in the cancellation callback

The logic gets completely stuck when this happens:

Stack trace below:
#0  0x77661424 in __kernel_vsyscall ()
#1  0x77337c3c in pthread_cond_wait ()
#2  0x773cebaa in g_cond_wait () from /usr/lib/libglib-2.0.so.0
#3  0x774c03cc in g_cancellable_disconnect () from /usr/lib/libgio-2.0.so.0
#4  0x76955d36 in connect_cancelled_cb (cancellable=0x78e055a0, self=0x78e0b590)
#5  0x77460982 in g_cclosure_marshal_VOID__VOIDv () from /usr/lib/libgobject-2.0.so.0
#6  0x7745ed8a in ?? () from /usr/lib/libgobject-2.0.so.0
#7  0x77478435 in g_signal_emit_valist () from /usr/lib/libgobject-2.0.so.0
#8  0x77478eb3 in g_signal_emit () from /usr/lib/libgobject-2.0.so.0
#9  0x774c01eb in g_cancellable_cancel () from /usr/lib/libgio-2.0.so.0
#10 0x776a0eab in mm_bearer_disconnect (self=0x78e0b590, callback=0x776c5980 <disconnect_ready>,
#11 0x776c57de in disconnect_next_bearer (ctx=0x78e12870) at mm-iface-modem-simple.c:898
#12 0x776c58d2 in disconnect_auth_ready (self=0x78df3048, res=0x78e06210, ctx=0x78e12870)
#13 0x774fed25 in g_simple_async_result_complete () from /usr/lib/libgio-2.0.so.0
#14 0x776a8c4e in authorize_ready (authp=0x78db68d0, res=0x76801638, simple=0x78e06210)
#15 0x774fed25 in g_simple_async_result_complete () from /usr/lib/libgio-2.0.so.0
#16 0x774fee3e in ?? () from /usr/lib/libgio-2.0.so.0
#17 0x7738a7a2 in ?? () from /usr/lib/libglib-2.0.so.0
#18 0x7738ce83 in g_main_context_dispatch () from /usr/lib/libglib-2.0.so.0
#19 0x7738d248 in ?? () from /usr/lib/libglib-2.0.so.0
#20 0x7738d6eb in g_main_loop_run () from /usr/lib/libglib-2.0.so.0
#21 0x77696a7d in main (argc=2, argv=0x7fbb1f04) at main.c:158

http://code.google.com/p/chromium-os/issues/detail?id=36448