allowing msg_name and msg_control

[Victor Stewart <v@nametag.social>]

RE Jen's proposed patch here
https://lore.kernel.org/io-uring/45d7558a-d0c8-4d3f-c63a-33fd2fb073a5@kernel.dk/

and RE what Stefan just mentioned in the "[PATCH 5.11] io_uring: don't
take fs for recvmsg/sendmsg" thread a few minutes ago... "Can't we
better remove these checks and allow msg_control? For me it's a
limitation that I would like to be removed."... which I coincidentally
just read when coming on here to advocate the same.

I also require this for a few vital performance use cases:

1) GSO (UDP_SEGMENT to sendmsg)
2) GRO (UDP_GRO from recvmsg)

GSO and GRO are super important for QUIC servers... essentially
bringing a 3-4x performance improvement that brings them in line with
TCP efficiency.

Would also allow the usage of...

3) MSG_ZEROCOPY (to receive the sock_extended_err from recvmsg)

it's only a single digit % performance gain for large sends (but a
minor crutch until we get registered buffer sendmsg / recvmsg, which I
plan on implementing).

So if there's an agreed upon plan on action I can take charge of all
the work and get this done ASAP.

#Victor