mlx5en: Don't set rate on SQs when the SQ is already stopped.

This can happen when connections are short lived and leads to
a firmware error printout in dmesg, syndrome 0x51cfb0, because
the SQ is in the wrong state.

Submitted by: hselasky@
Approved by: hselasky (mentor)
MFC after: 1 week
Sponsored by: Mellanox Technologies