net_sched: initialize net pointer inside tcf_exts_init()

net_sched: initialize net pointer inside tcf_exts_init()

BugLink: https://bugs.launchpad.net/bugs/1825942
For tcindex filter, it is too late to initialize the
net pointer in tcf_exts_validate(), as tcf_exts_get_net()
requires a non-NULL net pointer. We can just move its
initialization into tcf_exts_init(), which just requires
an additional parameter.

This makes the code in tcindex_alloc_perfect_hash()
prettier.

Cc: Jamal Hadi Salim <jhs@mojatatu.com>
Cc: Jiri Pirko <jiri@resnulli.us>
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
(cherry picked from commit 14215108a1fd7e002c0a1f9faf8fbaf41fdda50d)
Signed-off-by: Andrea Righi <andrea.righi@canonical.com>
Acked-by: Connor Kuehl <connor.kuehl@canonical.com>
Acked-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>