selftests/bpf: Run reuseport tests only with supported socket types

selftests/bpf: Run reuseport tests only with supported socket types

SOCKMAP and SOCKHASH map types can be used with reuseport BPF programs but
don't support yet storing UDP sockets. Instead of marking UDP tests with
SOCK{MAP,HASH} as skipped, don't run them at all.

Skipped test might signal that the test environment is not suitable for
running the test, while in reality the functionality is not implemented in
the kernel yet.

Before:

  sh# ./test_progs -t select_reuseport
  …
  #40 select_reuseport:OK
  Summary: 1/126 PASSED, 30 SKIPPED, 0 FAILED

After:

  sh# ./test_progs  -t select_reuseport
  …
  #40 select_reuseport:OK
  Summary: 1/98 PASSED, 2 SKIPPED, 0 FAILED

The remaining two skipped tests are SYN cookies tests, which will be
addressed in the subsequent patch.

Fixes: 9c6fb1e5aedd ("selftests/bpf: Extend SK_REUSEPORT tests to cover SOCKMAP/SOCKHASH")
Reported-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Jakub Sitnicki <jakub@cloudflare.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Martin KaFai Lau <kafai@fb.com>
Link: https://lore.kernel.org/bpf/20200224135327.121542-1-jakub@cloudflare.com