soccr: c/r ipv6 sockets which handles ipv4 connections

IPv6 listening sockets can accept both ipv4 and ipv6 connections,
in both cases a family of an accepted socket will be AF_INET6.

But we have to send tcp packets accoding with a connection type.

------------------------ grep Error ------------------------
(00.002320)     53: Debug: 		Will set rcv_wscale to 7
(00.002325)     53: Debug: 		Will turn timestamps on
(00.002331)     53: Debug: Will set mss clamp to 65495
(00.002338)     53: Debug: 	Restoring TCP 1 queue data 2 bytes
(00.002403)     53: Error (soccr/soccr.c:673): Unable to send a fin packet: libnet_write_raw_ipv6(): -1 bytes written (Network is unreachable)

(00.002434)     53: Error (criu/files.c:1191): Unable to open fd=3 id=0x6
(00.002506) Error (criu/cr-restore.c:2171): Restoring FAILED.
------------------------ ERROR OVER ------------------------

Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>

Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>