libbpf: Add extra BPF_PROG_TYPE check to bpf_object__probe_loading

eBPF has been backported for RHEL 7 w/ kernel 3.10-940+ [0]. However only
the following program types are supported [1]:

  BPF_PROG_TYPE_KPROBE
  BPF_PROG_TYPE_TRACEPOINT
  BPF_PROG_TYPE_PERF_EVENT

For libbpf this causes an EINVAL return during the bpf_object__probe_loading
call which only checks to see if programs of type BPF_PROG_TYPE_SOCKET_FILTER
can load.

The following will try BPF_PROG_TYPE_TRACEPOINT as a fallback attempt before
erroring out. BPF_PROG_TYPE_KPROBE was not a good candidate because on some
kernels it requires knowledge of the LINUX_VERSION_CODE.

  [0] https://www.redhat.com/en/blog/introduction-ebpf-red-hat-enterprise-linux-7
  [1] https://access.redhat.com/articles/3550581

Signed-off-by: Jonathan Edwards <[email protected]>
Signed-off-by: Daniel Borkmann <[email protected]>
Acked-by: Andrii Nakryiko <[email protected]>
Link: https://lore.kernel.org/bpf/[email protected]

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