uv_udp_set_ttl not supported for TizenRT

[pmarcinkiew]

TTL support is almost working for TizenRT but flag IPV6_UNICAST_HOPS is missing:

https://github.com/Samsung/libtuv/blob/master/src/unix/udp.c#L811

This issue prevents successful configuration of TTL in IoT.js for two tests.

test_dgram_setttl_client.js:

https://github.com/Samsung/iotjs/blob/master/test/run_pass/test_dgram_setttl_client.js#L36

test_dgram_setttl_server.js

https://github.com/Samsung/iotjs/blob/master/test/run_pass/test_dgram_setttl_server.js#L45

[glistening]

@pmarcinkiew I think uv_udp_set_ttl and uv_udp_get_ttl will work for IPv4 on TizenRT, and we need to support it.

[pmarcinkiew]

See: #92