ipv4: mode 0555 in ipv4_skeleton

vpnc on today's kernel says Cannot open "/proc/sys/net/ipv4/route/flush":
d--------- 0 root root 0 2008-08-26 11:32 /proc/sys/net/ipv4/route
d--------- 0 root root 0 2008-08-26 19:16 /proc/sys/net/ipv4/neigh

Signed-off-by: Hugh Dickins <hugh@veritas.com>
Acked-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>