Fix broken build in XenServer DDK 5.6.100-39265p.

Fix broken build in XenServer DDK 5.6.100-39265p.

Avoids errors like the following:

In file included from ./include/openvswitch/types.h:21,
                 from ./lib/vconn.h:21,
                 from tests/test-vconn.c:18:
/usr/include/sys/types.h:52: error: conflicting types for 'ino_t'
/usr/include/linux/types.h:14: error: previous declaration of 'ino_t' was here
/usr/include/sys/types.h:62: error: conflicting types for 'dev_t'
/usr/include/linux/types.h:13: error: previous declaration of 'dev_t' was here
/usr/include/sys/types.h:67: error: conflicting types for 'gid_t'
/usr/include/linux/types.h:27: error: previous declaration of 'gid_t' was here
/usr/include/sys/types.h:72: error: conflicting types for 'mode_t'
/usr/include/linux/types.h:15: error: previous declaration of 'mode_t' was here
/usr/include/sys/types.h:77: error: conflicting types for 'nlink_t'
/usr/include/linux/types.h:16: error: previous declaration of 'nlink_t' was here
/usr/include/sys/types.h:82: error: conflicting types for 'uid_t'
/usr/include/linux/types.h:26: error: previous declaration of 'uid_t' was here
/usr/include/sys/types.h:90: error: conflicting types for 'off_t'
/usr/include/linux/types.h:17: error: previous declaration of 'off_t' was here