Solaris: Default to fs_pathconf in afs_pathconf

Solaris: Default to fs_pathconf in afs_pathconf

Instead of returning EINVAL in afs_pathconf when we don't recognize the
pathconf command, return the result of fs_pathconf. fs_pathconf provides
sensible defaults or correctly represents a filesystem not implementing
a particular pathconf cmd; all in-tree (Open)Solaris filesystems call
fs_pathconf for unimplemented commands. Returning EINVAL allegedly
represents that the fileystem does not support pathconf at all.

Also, account for OpenSolaris adding another parameter to
pathconf-related calls.

Reviewed-on: http://gerrit.openafs.org/488
Tested-by: Derrick Brashear <shadow@dementia.org>
Reviewed-by: Derrick Brashear <shadow@dementia.org>