In libcasper, prefer to send a function index or service name over the IPC
channel to a zygote process, rather than sending a function pointer or
service pointer. This avoids transfering pointers between address spaces,
which while robust in this case (due to the zygote being forked() from the
parent) is not generally a good idea, especially in the presence of
increasingly popular control-flow integrity and pointer protection
mitigation schemes. With this change, ping(8) and other sandboxed tools
using libcasper for DNS resolution now work on architectures with tagged
memory again.

Reviewed by: oshogbo
MFC after: 1 week
Sponsored by: DARPA, AFRL