idpf: fix transaction timeouts on reset

Restore the call to idpf_vc_xn_shutdown() at the beginning of
idpf_vc_core_deinit() provided the function is not called on remove.
In the reset path the mailbox is destroyed, leading to all transactions
timing out.

Fixes: 09d0fb5c ("idpf: deinit virtchnl transaction manager after vport and vectors")
Reviewed-by: Larysa Zaremba <larysa.zaremba@intel.com>
Signed-off-by: Emil Tantilov <emil.s.tantilov@intel.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Tested-by: Krishneil Singh <krishneil.k.singh@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>