binmiscctl should use modfind instead of kldfind

kldfind() only matches kernel modules, so if you link imgact_binmisc directly
into the kernel, binmiscctl can't find it, tries to load it, and errors
out with:

Can't load imgact_binmisc kernel module: File exists

A quick search of other base commands shows that the correct procedure is to
call modfind(), and then try kldload() if that fails.

PR: 218593
Submitted by: Dan Nelson <dnelson_1901@yahoo.com>
MFC after: 1 week