common_probe_context.h: Put Individual Probe State (ips) into a union.

common_probe_context.h: Put Individual Probe State (ips) into a union.

Various probe handlers have dedicated fields in the common probe context
struct. Since the handlers cannot be active at the same time (on the same
cpu) these can just be put into a union to save space. In runtime code
when there might be ambiguity about which probe handler is running, the
CONTEXT->probe_type field can be used to check which field has actual
life data.