ovs-ofctl: Only allow usable protocols for group commands

parse_ofp_group_mod_str() may limit the usable protocols according
to the group and in particular its actions. However, without this
change ovs-ofctl ignores this calculation.

Signed-off-by: Simon Horman <simon.horman@netronome.com>
Acked-by: Jarno Rajahalme <jrajahalme@nicira.com>