Rebase of ANR2ME's sceHttp implementation

[hrydgard]

Rebase of #18003

Had to remove some duplicates from #19807 (derived from #18578), but I think it went okay.

Not tested much yet, will try to test a little before merge.

@anr2me

IMPORTANT INFO from anr2me:

This code is still experimental (just to get things to work), but my implementation is kinda wrong compared to JPCSP implementation.
My implementation is to use the parent simply as a template/base to initialize it's contents (ie. headers, userAgent, etc), thus any changes (ie. cookies, userAgent, etc) to the parent won't reflects existing children.
But later, i find out that JPCSP implementation is id-based relationship between parent-child similar to database's records relationship) and changes on the parent will reflects on it's children, thus cookies can be shared on multiple children (like a multi-tabs on most browsers).

So, this PR will need to be rewritten (probably using naett to support HTTPS too in the future), also need to do communication in a background thread to avoid stuttering the emulation.
So leaving this as a draft until i had the time to rewrite it (in case i lost my local copy due to bad sector).

[hrydgard]

@anr2me can you have a look at my "Add comment" commit? I don't understand what the function should return, heh.

EDIT: Actually never mind, that's the error case - I thought it returned 0 on success like most functions, but no heh.

[anr2me]

The returned value is similar to posix's inet_addr function.

Upon successful completion, inet_addr() shall return the Internet address. Otherwise, it shall return ( in_addr_t)(-1).