m/pkg/socksproxy: fix parsing of IPv6 addresses

ATYP=4 means that the address is an IPv6 address, of length 16 bytes.

Change-Id: Idc9701874a5b6a111cf15dbf55f82e1b8a2b68bc
Reviewed-on: https://review.monogon.dev/c/monogon/+/2949
Tested-by: Jenkins CI
Reviewed-by: Serge Bazanski <serge@monogon.tech>
Vouch-Run-CI: Serge Bazanski <serge@monogon.tech>
diff --git a/metropolis/pkg/socksproxy/protocol.go b/metropolis/pkg/socksproxy/protocol.go
index cb9ae0a..d920099 100644
--- a/metropolis/pkg/socksproxy/protocol.go
+++ b/metropolis/pkg/socksproxy/protocol.go
@@ -116,7 +116,7 @@
 	case 1:
 		addrBytes = make([]byte, 4)
 	case 4:
-		addrBytes = make([]byte, 4)
+		addrBytes = make([]byte, 16)
 	default:
 		return nil, errUnsupportedAddressType
 	}