For SEND_FAILED support, we need to keep around data chunk fragments
that have been acked, where other fragments of the same message
have not.  With this, Ardelle should be able to finish up the
SEND_FAILED support. 

Rip out our own HMAC-SHA1 and replace with crypto API.  
Can now choose hmac-sha1, hmac-md5, or none with regards to what
HMAC to use for cookie echo verification.

Code had hardcoded limits to the maximum stream that could be used, 
and consequent static data structures.   Now dynamically allocate
storage for the SSN maps until _after_ we know what they are.  
Protocols such as SIP want to use all possible streams.  

Makefiles no longer need to include Rules.make, which is currently an
empty file.  This patch removes it from the remaining Makefiles, and
removes the empty Rules.make file.

Traditionally, the individual components of a multipart module are
listed in <mod>-objs. Allow for using <mod>-y as well, as that turns
out to simplify declaring optional parts of multi-part modules, see
the converted examples in net/*/Makefile.

This change is backwards-compatible, i.e. not converted Makefiles
still work just fine.