archive_write_disk_posix: fix writing fflags broken in 8a1bd5c

The fixup list was erroneously assumed to be directories only.
Only in the case of critical file flags modification (e.g.
SF_IMMUTABLE on BSD systems), other file types (e.g. regular files
or symbolic links) may be added to the fixup list. We still need to
verify that we are writing to the correct file type, so compare the
archive entry file type with the file type of the file to be
modified.

Immutable flag no longer preserved during tar extraction on FreeBSD