Don't assume a default (currently 15) value for preloaded klds when

Don't assume a default (currently 15) value for preloaded klds when
loading hwpmc, but calculate at runtime and allocate the necessary space.
Also the current logic is wrong as it can lead to an endless loop.

Sponsored by:   Sandvine Incorporated
Reported by:    Ryan Stone <rstone at sandvine dot com>
Tested by:      Giovanni Trematerra
                <giovanni dot trematerra at gmail dot com>
Approved by:	re (kib)