tcp: fix formatting in sysctl_net_ipv4.c

Fix incorrectly formatted tcp_syn_linear_timeouts sysctl in the
ipv4_net_table.

Fixes: ccce324d ("tcp: make the first N SYN RTO backoffs linear")
Signed-off-by: David Morley <morleyd@google.com>
Signed-off-by: Neal Cardwell <ncardwell@google.com>
Tested-by: David Morley <morleyd@google.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>