netfilter: xt_osf: remove unused variable

While building with W=1 we got the warning:
net/netfilter/xt_osf.c:265:9: warning: variable 'loop_cont' set but not used

The local variable loop_cont was only initialized and then assigned a
value but was never used or checked after that.
While removing the variable, the case of OSFOPT_TS was not removed so
that it will serve as a reminder to us that we can do something in that
particular case.

Signed-off-by: Sudip Mukherjee <sudip.mukherjee@codethink.co.uk>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>