community/sniproxy: upgrade to 0.6.0

Modernize APKBUILD, update license, disable tests, add openrc subpkg

Several tests fail under abuild:

PASS: address_test
PASS: buffer_test
PASS: cfg_tokenizer_test
PASS: table_test
PASS: http_test
PASS: tls_test
PASS: binder_test
FAIL: connection_reset_test
PASS: bad_request_test
FAIL: fallback_test
FAIL: functional_test
FAIL: bind_source_test
FAIL: fd_limit_test
FAIL: ipv6_v6only_test
FAIL: proxy_header_test
SKIP: transparent_proxy_test
PASS: config_test
FAIL: reuseport_test
FAIL: reload_test
FAIL: slow_client_test
PASS: resolv_test
PASS: bad_dns_request_test

Running "make check" manually there's only one fail:

PASS: address_test
PASS: buffer_test
PASS: cfg_tokenizer_test
PASS: table_test
PASS: http_test
PASS: tls_test
PASS: binder_test
PASS: functional_test
PASS: bad_request_test
PASS: bind_source_test
PASS: connection_reset_test
PASS: fallback_test
PASS: fd_limit_test
PASS: ipv6_v6only_test
FAIL: proxy_header_test
PASS: reload_test
PASS: reuseport_test
PASS: slow_client_test
SKIP: transparent_proxy_test
PASS: config_test
PASS: resolv_test
PASS: bad_dns_request_test