[TCP] minisocks: Use kmemdup and LIMIT_NETDEBUG

Code diff stats:

[acme@newtoy net-2.6.20]$ codiff /tmp/tcp_minisocks.o.before /tmp/tcp_minisocks.o.after
/pub/scm/linux/kernel/git/acme/net-2.6.20/net/ipv4/tcp_minisocks.c:
  tcp_check_req |  -44
 1 function changed, 44 bytes removed
[acme@newtoy net-2.6.20]$

Signed-off-by: Arnaldo Carvalho de Melo <acme@mandriva.com>