docs: clarify documentation of uv_tcp_init_ex
docs: clarify documentation of uv_tcp_init_ex

I think this makes it clear that the flags can't contain any other
information.

PR-URL: https://github.com/libuv/libuv/pull/592
Reviewed-By: Ben Noordhuis <59bd0a3ff43b32849b319e645d4798d8a5d1e889@bnoordhuis.nl>

unknownbrackets/maxcso,unknownbrackets/maxcso,unknownbrackets/maxcso,unknownbrackets/maxcso,unknownbrackets/maxcso,unknownbrackets/maxcso,unknownbrackets/maxcso