add support for manually ignore functions

This commit adds the KPATCH_IGNORE_FUNC() macro for ignoring functions
that may change as a side effect of a change in another function.  The
WARN class of macros, for example, embed the line number in an
instruction, which will cause the function to be detected as changed
when, in fact, there has been no functional change.

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