kernel: nfp: flower: Fix a potential leak in nfp_tunnel_add_shared_mac()

In the Linux kernel, the following vulnerability has been resolved: nfp: flower: Fix a potential leak in nfptunneladdsharedmac idasimpleget returns an id between min 0 and max NFPMAXMACINDEX inclusive. So NFPMAXMACINDEX 0xff is a valid id. In order for the error handling path to work correctly, t...