driver module has been stopped since long time no interface is up
and dp_soc handle has been freed, but one virtual interface operation
still try to access invalid dp_soc from gp_cds_context, panic
happened.
set gp_cds_context->dp_soc to NULL if dp_soc is detached.
Change-Id: Icb2aa8bb15e309d8fcc749bafe37253c82a21f36
CRs-Fixed: 2413720