Reduce size of mymod and simplify kernel build process

[rapperskull]

I formatted this pull request so that you can merge the different changes independently.

• 02c895c6c6d7db43b5b9780767a5c1b7aeb168eb replaces kallsyms_on_each_symbol with kallsyms_lookup_name, resulting in a smaller mymod.ko file and a little bit faster execution times. This also means that no important part of the binary sits at offset 0x2000, and the whole file is less than 12 KB (only 3 pages).
• 11cd155b1e8eff36b1810d7934b11710912ea555 simplifies the patch, since there's no need to set a specific version.
• ce0551ded1f0485f5281ac92ab77306f621deffb removes the patch altogether, switching to setting an environment variable. The advantage is that the build process is simplified, the downside is a slightly longer build time and an inconvenient command to execute.

[polygraphene]

Thank you for good work!

https://github.com/polygraphene/DirtyPipe-Android/commit/02c895c6c6d7db43b5b9780767a5c1b7aeb168eb

I didn't know kallsyms_lookup_name. Looks a good change.

I prefer simplified patch version. Because I don't know how to cherry-pick commits from PR, can you change it to include only https://github.com/polygraphene/DirtyPipe-Android/commit/02c895c6c6d7db43b5b9780767a5c1b7aeb168eb and https://github.com/polygraphene/DirtyPipe-Android/commit/11cd155b1e8eff36b1810d7934b11710912ea555?

[rapperskull]

Done