tc: m_csum: parse index argument correctly

tc: m_csum: parse index argument correctly

'action csum index 1' is a valid cli according to TC's
architecture. Fix the grammar parsing to accept it.

tdc tests:
1..24
ok 1 6d84 - Add csum iph action
ok 2 1862 - Add csum ip4h action
ok 3 15c6 - Add csum ipv4h action
ok 4 bf47 - Add csum icmp action
ok 5 cc1d - Add csum igmp action
ok 6 bccc - Add csum foobar action
ok 7 3bb4 - Add csum tcp action
ok 8 759c - Add csum udp action
ok 9 bdb6 - Add csum udp xor iph action
ok 10 c220 - Add csum udplite action
ok 11 8993 - Add csum sctp action
ok 12 b138 - Add csum ip & icmp action
ok 13 eeda - Add csum ip & sctp action
ok 14 0017 - Add csum udp or tcp action
ok 15 b10b - Add all 7 csum actions
ok 16 ce92 - Add csum udp action with cookie
ok 17 912f - Add csum icmp action with large cookie
ok 18 879b - Add batch of 32 csum tcp actions
ok 19 b4e9 - Delete batch of 32 csum actions
ok 20 0015 - Add batch of 32 csum tcp actions with large cookies
ok 21 989e - Delete batch of 32 csum actions with large cookies
ok 22 d128 - Replace csum action with invalid goto chain control
ok 23 eaf0 - Add csum iph action with no_percpu flag
ok 24 c619 - Reference csum action object in filter

Fixes: 3822cc986cc3 ("tc: add ACT_CSUM action support (csum)")
Reviewed-by: Jamal Hadi Salim <jhs@mojatatu.com>
Signed-off-by: Pedro Tammela <pctammela@mojatatu.com>
Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>