Fix build break in xen

Build breaks in xen ddk as endian.h does not have be64toh and its friends defined there.
Replace them with macros that does the same functionality

Signed-off-by: Anirban Chakraborty <abchak@juniper.com>
Merge pull request #581 from anirban-c/master

Fix build break in xen
Merge remote branch 'upstream/master'
* Address review comments
* Add more interface activate deactivate test case for nexthop deletion