srm-client: by default only delegate for srmcp with 3rd-party copies

Currently, the SRM client will delegate for all calls.  This patch
updates the default behaviour so it doesn't delegate, except for
srmcp involving an SRM-endpoint and some remote end-point.

Patch: https://rb.dcache.org/r/7031/
Acked-by: Karsten Schwank
Requires-book: no
Requires-notes: yes