netfilter: nf_tables: fully validate NFT_DATA_VALUE on store to data registers

In the Linux kernel, the following vulnerability has been resolved: netfilter: nf_tables: fully validate NFT_DATA_VALUE on store to data registers register store validation for NFT_DATA_VALUE is conditional, however, the datatype is always either NFT_DATA_VALUE or NFT_DATA_VERDICT. This only requires a new helper function to infer the register type from the set datatype so this conditional check can be removed. Otherwise, pointer to chain object can be leaked through the registers.