main_process: close the channel receivers.

[ipuustin]

It looks like libcontainer (at least when used from runwasi) is leaking three FDs for every container creation. This becomes a problem in Wasm use cases, where a single process may spawn a large number of Wasm containers. The lsof output looks like this:

...

container 364412 root  649u  unix 0x00000000ff880cf0       0t0  3539568 type=SEQPACKET (CONNECTED)
container 364412 root  650u  unix 0x000000003b11c72f       0t0  3537567 type=SEQPACKET (CONNECTED)
container 364412 root  651u  unix 0x0000000059949a57       0t0  3539570 type=SEQPACKET (CONNECTED)
container 364412 root  652u  unix 0x00000000c24f282c       0t0  3527349 type=SEQPACKET (CONNECTED)
container 364412 root  653u  unix 0x000000004a43cc7c       0t0  3537576 type=SEQPACKET (CONNECTED)
container 364412 root  654u  unix 0x000000004e420b32       0t0  3527351 type=SEQPACKET (CONNECTED)
container 364412 root  655u  unix 0x00000000c8e66c94       0t0  3537569 type=SEQPACKET (CONNECTED)
container 364412 root  656u  unix 0x00000000e91c2358       0t0  3537586 type=SEQPACKET (CONNECTED)
container 364412 root  657u  unix 0x000000006fc2e3b2       0t0  3537571 type=SEQPACKET (CONNECTED)
container 364412 root  658u  unix 0x000000001834ff2e       0t0  3537578 type=SEQPACKET (CONNECTED)
container 364412 root  659u  unix 0x00000000f0765edf       0t0  3537595 type=SEQPACKET (CONNECTED)
container 364412 root  660u  unix 0x000000004c210c5b       0t0  3537580 type=SEQPACKET (CONNECTED)
container 364412 root  661u  unix 0x0000000079f6e005       0t0  3537588 type=SEQPACKET (CONNECTED)
container 364412 root  662u  unix 0x00000000d5be89be       0t0  3539578 type=SEQPACKET (CONNECTED)
container 364412 root  663u  unix 0x000000003dc2d14f       0t0  3537590 type=SEQPACKET (CONNECTED)
container 364412 root  664u  unix 0x00000000d71d68b7       0t0  3537597 type=SEQPACKET (CONNECTED)
container 364412 root  665u  unix 0x00000000666f45e0       0t0  3539586 type=SEQPACKET (CONNECTED)
container 364412 root  666u  unix 0x000000007db0b87d       0t0  3537599 type=SEQPACKET (CONNECTED)
container 364412 root  667u  unix 0x00000000822c2187       0t0  3539580 type=SEQPACKET (CONNECTED)
container 364412 root  668u  unix 0x00000000a6ce888a       0t0  3539595 type=SEQPACKET (CONNECTED)
container 364412 root  669u  unix 0x0000000074afe56b       0t0  3539582 type=SEQPACKET (CONNECTED)
container 364412 root  670u  unix 0x0000000058dfe294       0t0  3539588 type=SEQPACKET (CONNECTED)
container 364412 root  671u  unix 0x0000000053a89328       0t0  3539604 type=SEQPACKET (CONNECTED)
container 364412 root  672u  unix 0x0000000049ce8f4b       0t0  3539590 type=SEQPACKET (CONNECTED)
...

This PR closes the receiving ends for the Youki sockets. The number of open sockets goes down and I'm able to run over a thousand containers from one process. I'm not familiar enough with Youki to be certain that this doesn't have any side effects, though.

[utam0k]

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