scripts/coccinelle: add some more coccinelle tests

Add some useful static code analysis scripts for coccinelle
copied from the Linux kernel v4.14-rc8:

Warn on check against NULL before calling free.
scripts/coccinelle/free/ifnullfree.cocci

Detect superfluous NULL check for list iterator.
scripts/coccinelle/iterators/itnull.cocci

Check if list iterator is reassigned.
scripts/coccinelle/iterators/list_entry_update.cocci

Check if list iterator is used after loop.
scripts/coccinelle/iterators/use_after_iter.cocci

Find wrong argument of sizeof in allocation function:
scripts/coccinelle/misc/badty.cocci

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>