Skip KTLS test if the host kernel is older than 5.11
The ktls.sh test currently only supports kernel 5.11+. This needs to
be checked at run time, as the koji builder might be using a different
version of kernel on the host than the one indicated by the
kernel-devel package.
Resolves: #2247135
Signed-off-by: Daiki Ueno <dueno@redhat.com>