lockf: remove lf_inode from struct lockf_entry

The UFS-specific struct inode cannot be used in generic advisory lock
code. It was probably used as a shortcut for the debugging, as the
remnants of the code around it indicates.

Use somewhat more verbose and less concentrated, but universal,
VOP_PRINT(), where needed.

Reviewed by: markj, rmacklem
Sponsored by: The FreeBSD Foundation
MFC after: 1 week
Differential revision: https://reviews.freebsd.org/D34756