tcp: unset TCP_REPAIR at the last moment after unlocking network (v2)

TCP_REPAIR should be droppet when a network is unlocked.
A network should be unlocked at the last moment, because
after this moment restore must not failed, otherwise a state of
a tcp connection can be changed and a state of one side in our image
will be invalid.

v2: use xremalloc instead of mmap and remmap

Signed-off-by: Andrey Vagin <avagin@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>