shared/gatt-client: Ignore orphaned characteristics

shared/gatt-client: Ignore orphaned characteristics

The gatt discovery proceedure simplification to discover all
characteristics at once has exposed a device side issue where some
device implementation reports orphaned characteristics.  While this
technically shouldn't be allowed, some instances of this were observed
(namely on some Android phones).

The fix is to simply skip over orphaned characteristics and continue
with everything else that is valid.

This has been tested as part of the Android CTS tests against an
affected platform and was confirmed to have worked around the issue.

Signed-off-by: Anuj Jain <anuj01.jain@samsung.com>
Signed-off-by: Ayush Garg <ayush.garg@samsung.com>