[netstack] Make recvmsg(2) call to host in hostinet even if dst is empty.

We want to make the recvmsg syscall to the host regardless of if the dst is
empty or not so that:
- Host can populate the control messages if necessary.
- Host can return sender address.
- Host can return appropriate errors.

Earlier because we were using the IOSequence.CopyOutFrom() API, the usermem
package does not even call the Reader function if the destination is empty (as
an optimization).

PiperOrigin-RevId: 347684566

0 files changed, 0 insertions, 0 deletions