Bump kldxref's MAXSEGS to 16, to stop complaints about the kernel
supposedly having too many segments, when lld 11 links it. Such kernels
should load just fine.

Note that we may still do some tweaking of our kernel linker scripts, to
lower the number of segments, although the exact benefit is not entirely
clear.

PR: 252459

(cherry picked from commit 05c312a339096ac54d404029ddfcd0114d452a4c)