elements/CoDel: convert from raw division to int_divide

The compiler was promoting some of the operations here to wider types.  This
meant that a kernel module with CoDel would fail to link against __divdi3.

Instead, use the helper functions in click/integers.hh

Signed-off-by: Derrick Pallas <pallas@meraki.com>
Include packet_anno header

Needed for FIRST_TIMESTAMP_ANNO
NOACK value
16-bit txflags
linuxmodule/FromDevice: replace assert with skb_share_check

It isn't clear that this assertion holds in general, so just Do the Right
Thing instead.  If the check returns NULL, the original SKB has already lost
a ref, so report that it was handled.
click/string: clear dangling pointer on String::deref

In order to make use-after-free of Strings fail more quickly, this change
blows away _r.memo on String::deref(), since we should no longer hold a
reference to it.  Additionally, it asserts that the memo_t's refcount is not
zero when deref is invoked, since the caller should have a valid reference
at that point, and also that the refcount is zero when the memo_t is
deleted.
OML support and configuration files for experimentation on Backpressure, etc