octeontx2-pf: tc: fix egress ratelimiting

octeontx2-pf: tc: fix egress ratelimiting

The egress rate calculation computes an incorrect mantissa and exponent,
causing up to ~50% deviation from the configured rate at lower speeds.

Rework the computation to follow the hardware rate formula:

	rate = 2 * (1 + mantissa/256) * 2^exp / (1 << div_exp)

Keep div_exp = 0 and derive exp and mantissa from half of the requested
rate. Rates below 2 Mbps are floored to the smallest encodable step
(exp = 0, mantissa = 0).

Fixes: e638a83f167e ("octeontx2-pf: TC_MATCHALL egress ratelimiting offload")
Signed-off-by: Hariprasad Kelam <hkelam@marvell.com>
Signed-off-by: Nitin Shetty J <nshettyj@marvell.com>
Link: https://patch.msgid.link/20260717084349.2227796-1-nshettyj@marvell.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>