selftests/bpf: Introduce cond_break_label

Add a new cond_break_label macro that jumps to the specified label when
the cond_break termination check fires, and allows us to better handle
the uncontrolled termination of the loop.

Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Link: https://lore.kernel.org/r/20250306035431.2186189-2-memxor@gmail.com


Signed-off-by: Alexei Starovoitov <ast@kernel.org>