Fix smbfs to not zero out statfs f_flags field. Previously, this
made getmntinfo() return empty flags for smbfs filesystems when
called with MNT_WAIT. It's not visible with mount(8), since it uses
MNT_NOWAIT, but broke autounmount(8) operation.

PR:		195161
Differential Revision:	https://reviews.freebsd.org/D1194
Reviewed by:	kib@
MFC after:	1 month
Sponsored by:	The FreeBSD Foundation
Partially reconstruct Active/Standby clusting.

In this mode one head is in Active state, supporting all commands, while
another is in Standby state, supporting only minimal LUN discovery subset.

It is still incomplete since Standby state requires reservation support,
which is impossible to do right without having interlink between heads.
But it allows to run some basic experiments.
Log errors for absent LUNs too.

MFC after:	1 week
Fix build for certain MIPS kernels hiding an unused variable under #ifndef.