libbpf: Support BTF_KIND_FLOAT during type compatibility checks in CO-RE

Add BTF_KIND_FLOAT support when doing CO-RE field type compatibility check.
Without this, relocations against float/double fields will fail.

Also adjust one error message to emit instruction index instead of less
convenient instruction byte offset.

Fixes: 22541a9e ("libbpf: Add BTF_KIND_FLOAT support")
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Lorenz Bauer <lmb@cloudflare.com>
Link: https://lore.kernel.org/bpf/20210426192949.416837-3-andrii@kernel.org