expr: fix registers datatypes

Registers datatypes must be enum nft_registers.

Pablo Neira says:
<< From the kernel representation point of view, it doesn't make any sense to have set both sreg and dreg, but we should not make such assumption from userspace. If the user sets both sreg and dreg, it's wrong and the kernel should reply -EINVAL so the user knows that it has to fix its userspace code. This requires a bit more memory in userspace, but we don't have the memory restrictions that we have in kernelspace, so a bit more consumption won't harm. >>

So, while at it, delete the meta expr union for registers.

---
 src/expr/cmp.c  |    2 +-
 src/expr/meta.c |    6 ++----
 2 files changed, 3 insertions(+), 5 deletions(-)

index 246f22f..ab244ac 100644
@@ -26,7 +26,7 @@
 
 struct nft_expr_cmp {
 	union nft_data_reg	data;
-	uint8_t			sreg;	/* enum nft_registers */
+	enum nft_registers	sreg;
 	uint8_t			op;	/* enum nft_cmp_ops */
 };
 

index 490d64a..7fd0af1 100644
@@ -28,10 +28,8 @@
 
 struct nft_expr_meta {
 	uint8_t			key;	/* enum nft_meta_keys */
-	union {
-		uint8_t		dreg;	/* enum nft_registers */
-		uint8_t		sreg;   /* enum nft_registers */
-	};
+	enum nft_registers	dreg;
+	enum nft_registers	sreg;
 };
 
 static int

Need a fix for this in master, I forgot to specify. I just sent several patches. Thanks anyway.