netfilter: xt_TCPOPTSTRIP: signed tcphoff for ipv6_skip_exthdr() retval

if tcphoff remains unsigned, a negative ipv6_skip_exthdr() return value will
go unnoticed,

Signed-off-by: Roel Kluin <12o3l@tiscali.nl>
Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
1 file changed