feature: add support for tcp/udp bind.

[alonbg]

+tests

[alonbg]

Hi @agentzh
Some tests keep failing although all tests pass on my local.
Please advise (maybe on a better way to write them :). Thanks!

[bjne]

What is the status here? Nice effort, but code does not build.

[alonbg]

@agentzh you suggested having ip_transparent in the setoption api. I'm really not sure this is the way to go since there is a dependency between ip_transparent and bind. As in proxy_bind address [transparent] | off; directive which sets sets pc-local which in turn is a condition for checking pc->transparent value. In other words, binding to a local address is a mandatory condition for setting the ip_transparent socket option.
Maybe also in our case transparent should be a bind() option instead of a separate api.
What do you think ?

[splitice]

I tend to agree with @alonbg, its closer to the nginx semantics too which is appealing to me.