walk: reduce load while idle

[SammyRamone]

Proposed changes

Without this fix, the walking will create a large CPU load until it first recieves goals. Additionally, it is just unnecessary to compute the IK while the walking is idle.

Related issues

Necessary checks

• [ ] Update package version
• [ ] Run catkin build
• [ ] Write documentation
• [ ] Create issues for future work
• [ ] Test on your machine
• [ ] Test on the robot
• [ ] Put the PR on our Project board