kdump(8): Add more support for printing flag etc. names.

kdump(8): Add more support for printing flag etc. names.

* New support for: eaccess() modes, faccessat() modes and atflag,
    fchmodat() atflag, fchownat() atflag, fstatat() atflag,
    linkat() atflag, unlinkat() atflag, utimensat() atflag,
    getvfsstat() flags, lchflags() flags, chflagsat() flags and atflag,
    kenv() actions, usched_set() commands, sys_checkpoint() types,
    procctl() commands, mountctl() operations, and varsym_{list,set}()
    levels.

* Fix flags printing in chflags() and fchflags().

* Better separate mount() and getfsstat() flags definitions.

* Adjust grepping for fcntl() commands send/recvmsg() etc. flags to
    include flags with more than one underscore in their name, like
    F_DUPFD_CLOEXEC.

Still missing: extexit()'s 'how' argument.