libbpf: Start v1.8 development cycle

libbpf 1.7.0 has been released [1].

Update libbpf.map and libbpf_verson.h to start v1.8 development cycle.

[1] https://github.com/libbpf/libbpf/releases/tag/v1.7.0

Signed-off-by: Ihor Solodrai <ihor.solodrai@linux.dev>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20260316163916.2822081-1-ihor.solodrai@linux.dev