magic_write: Translate struct page to virtual address in BPF programs

[AlonZivony]

In my work on the issue of missing magic_write event during sendfile syscall (#1357) I concluded that given the fact that we can't read from files directly the data, the best thing we have in the flow of the code in the kernel is access to pages that include the data (through the pipe_inode_info struct).
So, to be able to read the data from a page, a method to convert struct page to its matching virtual address is required.
It is a bit complicated to implement because of different physical memory models available and different architecture implementations, but it should be possible using defines, kconfig and globals (#1506 #1504 #1505).

[yanivagman]

This is more an implementation discussion than an issue in tracee.
Converting to discussion