ext4dist: code cleanup (#2181) (#2206)
ext4dist: code cleanup (#2181) (#2206)

* ext4dist: code cleanup (#2181)

 - Dynamically handle different ext4_file_operations
   (avoid wasting extra cycles).

 - make the code pep8 compliant

 - clarify comments

* ext4dist: fix: properly support kernels without ext4_file_read_iter()

Signed-off-by: Andrea Righi <243bc7e273657b4ad9a7ca12a3b3ad7b5bb1c892@gmail.com>

mcaleavya/bcc,tuxology/bcc,iovisor/bcc,mcaleavya/bcc,mcaleavya/bcc,brendangregg/bcc,iovisor/bcc,tuxology/bcc,iovisor/bcc,brendangregg/bcc,tuxology/bcc,brendangregg/bcc,tuxology/bcc,iovisor/bcc,mcaleavya/bcc,brendangregg/bcc,tuxology/bcc,mcaleavya/bcc,brendangregg/bcc,iovisor/bcc