[OpenAFS] Recent Fedora kmod issues

[Jon Stanley]

In openafs-kmodtool, it outputs an RPM header that the kmod package
uses. However, it has two problematic lines:

Requires(post): /sbin/depmod
Requires(postun): /sbin/depmod

In recent versions of Fedora, and in RHEL7+, there is no longer a
distinction between /sbin and /usr/sbin, and the former is a symlink
to the latter. Therefore, the RPM database has kmod as providing
/usr/sbin/depmod, not /sbin/depmod, and therefore OpenAFS kmod will
not install.

A simple change to have those lines reference /usr/sbin/depmod worked.
I think that the logic probably needs to be conditionalized such that
on RHEL6 and below, we use /sbin/depmod, and Fedora >=17 and RHEL >=7
we use /usr/sbin/depmod.