change matching criteria for NULL sym

Right now the matching criteria for the NULL sym is type LOCAL and shndx
UNDEF.  Unfortunately, that would also match any new LOCAL symbol
added to the symbol table with uninit'd sym.* fields i.e. the upcoming
__kpatch_strings and .kpatch.strings symbols.

Change the matching criteria to be symbols that have a zero-length name;
a property unique to the NULL sym.

Signed-off-by: Seth Jennings <sjenning@redhat.com>
symbol location verification support

This commit introduces functionality to verify the location of symbols
used in both the patch and dynrelas sections.  It adds significant
protection from mismatches between the base and running kernels.

Signed-off-by: Seth Jennings <sjenning@redhat.com>
review fixups

Signed-off-by: Seth Jennings <sjenning@redhat.com>
Merge pull request #209 from spartacus06/symbol-location-verification

Symbol location verification