MFC r231505,231520:

MFC r231505,231520:

 Introduce a new NET_RT_IFLISTL API to query the address list.  It works
 on extended and extensible structs if_msghdrl and ifa_msghdrl.  This
 will allow us to extend both the msghdrl structs and eventually if_data
 in the future without breaking the ABI.

 The MFC is just to provide the new API to old stable branches to make
 updating and if needed downgrading a lot easier for updates to 10.

 Bump __FreeBSD_version to allow ports to more easily detect the new API.

git-svn-id: svn://svn.freebsd.org/base/stable/8@231769 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f