enic: Move function from header file to c file

enic: Move function from header file to c file

Moves cq_enet_rq_desc_dec from cq_enet_desc.h to enic_rq.c.
This is in preparation for enic extended completion queue
enabling.

Co-developed-by: Nelson Escobar <neescoba@cisco.com>
Signed-off-by: Nelson Escobar <neescoba@cisco.com>
Co-developed-by: John Daley <johndale@cisco.com>
Signed-off-by: John Daley <johndale@cisco.com>
Signed-off-by: Satish Kharat <satishkh@cisco.com>
Link: https://patch.msgid.link/20250304-enic_cleanup_and_ext_cq-v2-1-85804263dad8@cisco.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>