test: improve macro-hooks patch

Restore aio_max_nr to its original value when unloading.

Also move the location of the patch hunk to be not at the end of the
file.  Otherwise we hit a weird combinediff bug which results in the
diff's context being removed.
make "descriptor" a special static local variable

The "descriptor" static local variables and their containing __verbose
section are used for dynamic debug printks.  They should be considered
as special static local variable symbols because they have the same
requirements: they should never be correlated and they should only be
included if referenced by an included function.
allow shadow functions to be called from modules

Fixes an issue where attempting to call the shadow functions from a
module results in modpost failures:

    ERROR: "kpatch_shadow_get" [net/mac80211/mac80211.ko] undefined!
    ERROR: "kpatch_shadow_alloc" [net/mac80211/mac80211.ko] undefined!

LDFLAGS_MODULE is apparently not really needed.
Merge pull request #436 from jpoimboe/descriptor

make "descriptor" a special static local variable
Merge pull request #441 from jpoimboe/module-shadow

allow shadow functions to be called from modules
fix object unlink error handling

Fix the object unlink error handling so that each function cleans up
after itself properly.

Also use find_symbol() instead of __symbol_get() to make cleanup easier.
When patching a module we don't need a reference to each symbol, since
we already have done a try_module_get() on the module.

Fixes #392.