add KPATCH_WARN_*_LINE macros

WARN macros are problematic because they embed the line number in an
instruction.  As a result, when a function is changed higher in a file,
the line numbers for any WARN calls below that function in the file can
result in unnecessarily changed functions.

These macros allow a patch author to hard code the line numbers in WARN
macros to prevent functions from otherwise changing and getting pulled
into a patch module unnecessarily.
Merge pull request #303 from jpoimboe/warn-macros

add KPATCH_WARN_*_LINE macros