Correct compilation of osnet/dist/uts/common/dtrace/dtrace.c under Clang

Add missing const keywords in dtrace_strncmp().

Initialize lim1 and lim2 to zero always. This prevents a false positive
about potentially unset but used variable.

This could be done with -W flags, but they are incompatible between
compilers.

This is a step forward functional MKLLVM=yes HAVE_LLVM=yes build.

Sponsored by <The NetBSD Foundation>

(kamil)