FreeBSD_HEAD_arm64 - Build #609 - Fixed

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FreeBSD_HEAD_arm64 - Build #609 - Fixed:

Build information: https://jenkins.FreeBSD.org/job/FreeBSD_HEAD_arm64/609/
Full change log: https://jenkins.FreeBSD.org/job/FreeBSD_HEAD_arm64/609/changes
Full build log: https://jenkins.FreeBSD.org/job/FreeBSD_HEAD_arm64/609/console

Change summaries:

285616 by kib:
Do not use atomic_swap_int(9), it is not available on all
architectures.  Atomic_cmpset_int(9) is a direct replacement, due to
loop.  The change fixes arm, arm64, mips an sparc64, which lack
atomic_swap().

Suggested and reviewed by:	alc
Sponsored by:	The FreeBSD Foundation
MFC after:	2 weeks

285615 by jmg:
fix the docs, the number of frags per inode (NFPI) changed in r228794
to 2 from 4, but the man page didn't get updated...

other minor changes to make igor happy...

MFC after:	3 days