kernel linker: Disable local sym resolution by default

[emaste]

Summary

In 95c20faf11a1 and ecd8245e0d77 kib introduced support to have the
kernel linker stop resolving local symbols from other files, but did
not enable it by default to avoid surprises.  Flip the default now,
in advance of FreeBSD 15.0.  The debug.link_elf_leak_locals sysctl
is available to revert to the previous behaviour if necessary.

[emaste]

PR: 207898

[emaste]

whole patch