MFC r329265, r329384

r329265:
Implement .vop_pathconf and .vop_getacl for the .zfs ctldir

zfsctl_common_pathconf will report all the same variables that regular ZFS
volumes report. zfsctl_common_getacl will report an ACL equivalent to 555,
except that you can't read xattrs or edit attributes.

Fixes a bug where "ls .zfs" will occasionally print something like:
ls: .zfs/.: Operation not supported

PR: 225793
Reviewed by: avg
Sponsored by: Spectra Logic Corp
Differential Revision: https://reviews.freebsd.org/D14365

r329384:
Handle generic pathconf attributes in the .zfs ctldir

MFC instructions: change the value of _PC_LINK_MAX to INT_MAX

Reported by: jhb
X-MFC-With: 329265
Sponsored by: Spectra Logic Corp