[Docs][CodeGenerator][eBPF] Correct the values for BPF_X and BPF_K

[udknight]

Summary

Fix the values of BPF_X and BPF_K according to BPFInstrFormats.td:
"
def BPF_K : BPFSrcType<0x0>;
def BPF_X : BPFSrcType<0x1>;
"

The right value for BPF_X is 0x1, and the right value for BPF_K is 0x0.

[yonghong-song]

Thanks for the fix! Please go ahead to land by yourself if you have write permission. Otherwise, let me know I can land for you.

[udknight]

In D61512#1489892, @yonghong-song wrote:

Thanks for the fix! Please go ahead to land by yourself if you have write permission. Otherwise, let me know I can land for you.

No, I don't have write permission, so please land it for me.

Thanks!

[yonghong-song]

merged. https://reviews.llvm.org/rL359904

docs/CodeGenerator.rst

::
   (unused)   0x6
   BPF_ALU64  0x7
 
 When BPF_CLASS(code) == BPF_ALU or BPF_ALU64 or BPF_JMP,
 4th bit encodes source operand
 
 ::
 
-  BPF_X     0x0  use src_reg register as source operand
-  BPF_K     0x1  use 32 bit immediate as source operand
+  BPF_X     0x1  use src_reg register as source operand
+  BPF_K     0x0  use 32 bit immediate as source operand
 
 and four MSB bits store operation code
 
 ::
 
   BPF_ADD   0x0  add
   BPF_SUB   0x1  subtract
   BPF_MUL   0x2  multiply