sysutils/moosefs2-master: fix build of client on GCC architectures

sustained_inodes.c: In function 'sinodes_pid_inodes':
sustained_inodes.c:224: error: 'struct kinfo_file' has no member named 'kf_un'
sustained_inodes.c:225: error: 'struct kinfo_file' has no member named 'kf_un'

MFH: 2020Q4