Setting it in load() excludes users of ELF::Loader that don't actually
call load() but only use the Loader for symbolication purposes.
Perhaps the factoring here is not ideal.
If a buffer smaller than Elf32_Ehdr was passed to Image, header()
would do an out-of-bounds read.
Make parse() check for that. Make most Image methods assert that the image
is_valid(). For that to work, set m_valid early in Image::parse()
instead of only at its end.
Also reorder a few things so that the fuzzer doesn't hit (valid)
assertions, which were harmless from a security PoV but which still
allowed userspace to crash the kernel with an invalid ELF file.
Make dbgprintf()s configurable at run time so that the fuzzer doesn't
produce lots of logspam.
