nc: use symbolic SHUT_WR instead of literal 1

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
nc: exit when both stdin and network are closed.

function                                             old     new   delta
nc_main                                             1051    1042      -9
readwrite                                            943     887     -56

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
nc: remove some dead code

function                                             old     new   delta
readwrite                                            887     841     -46

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
logread: intercept all fatal signals, not just SIGINT

function                                             old     new   delta
interrupted                                           27      20      -7

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
iplink: fix build error (IFLA_VLAN_PROTOCOL defined before include)

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>