ipsec-tools: build racoon XAUTH client

This patch introduces the necessary build infrastructure to allow
racoon to act as an XAUTH client.  Specifically, it adds the XAUTH
related source files to the build, defines necessary macros, includes
additional header files and disables certain XAUTH server code, such
as accounting support, which is not required for an XAUTH client nor
supported by bionic.

picked from
https://android-review.googlesource.com/#/c/17829/
Merge "ipsec-tools: build racoon XAUTH client" into gingerbread