[ICMP]: Optimize icmp_socket usage.

Use this macro only once in a function to save a bit of space.

add/remove: 0/0 grow/shrink: 0/3 up/down: 0/-98 (-98)
function                                     old     new   delta
icmp_reply                                   562     561      -1
icmp_push_reply                              305     258     -47
icmp_init                                    273     223     -50

Signed-off-by: Denis V. Lunev <den@openvz.org>
Acked-by: Daniel Lezcano <dlezcano@fr.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>