doc: update kernel guide links

The patch submission and coding style guide links were outdated.

HACKING

@@ -11,7 +11,8 @@ In order to ease the inclusion of your patch, it's important to follow
 some rules, otherwise it will likely be rejected by maintainers.
 
 iwd rules for submitting patches follow most of the rules used by Linux kernel
-(https://www.kernel.org/doc/Documentation/SubmittingPatches) with some remarks:
+(https://www.kernel.org/doc/Documentation/process/submitting-patches.rst) with
+some remarks:
 
 1) Do *not* add "Signed-off-by" lines in your commit messages. iwd does not
 use them, so including them is actually an error.

doc/coding-style.txt

@@ -9,8 +9,8 @@ to help your code survive under maintainer's fastidious eyes so that you
 can get a passport for your patch ASAP.
 
 First of all, the Wireless daemon coding style must follow every rule for
-Linux kernel (http://www.kernel.org/doc/Documentation/CodingStyle).  There
-also exists a tool named checkpatch.pl to help you check the compliance
+Linux kernel (http://www.kernel.org/doc/Documentation/process/coding-style.rst).
+There also exists a tool named checkpatch.pl to help you check the compliance
 with it. Just type "checkpatch.pl --no-tree --no-signoff patch_name" to
 check your patch.