tools/bpf: adjust rlimit RLIMIT_MEMLOCK for test_tcpbpf_user

The default rlimit RLIMIT_MEMLOCK is 64KB. In certain cases,
e.g. in a test machine mimicking our production system, this test may
fail due to unable to charge the required memory for map creation:
   # ./test_tcpbpf_user
   libbpf: failed to create map (name: 'global_map'): Operation not permitted
   libbpf: failed to load object 'test_tcpbpf_kern.o'
   FAILED: load_bpf_file failed for: test_tcpbpf_kern.o

Changing the default rlimit RLIMIT_MEMLOCK to unlimited makes
the test always pass.

Signed-off-by: Yonghong Song <yhs@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>