igb: reject invalid external timestamp requests for 82580-based HW

The igb_ptp_feature_enable_82580 function correctly checks that unknown
flags are not passed to the function. However, it does not actually check
PTP_RISING_EDGE or PTP_FALLING_EDGE when configuring the external timestamp
function.

The data sheet for the 82580 product says:

  Upon a change in the input level of one of the SDP pins that was
  configured to detect Time stamp events using the TSSDP register, a time
  stamp of the system time is captured into one of the two auxiliary time
  stamp registers (AUXSTMPL/H0 or AUXSTMPL/H1).

  For example to define timestamping of events in the AUXSTMPL0 and
  AUXSTMPH0 registers, Software should:

  1. Set the TSSDP.AUX0_SDP_SEL field to select the SDP pin that detects
     the level change and set the TSSDP.AUX0_TS_SDP_EN bit to 1.

  2. Set the TSAUXC.EN_TS0 bit to 1 to enable timestamping

The same paragraph is in the i350 and i354 data sheets.

The wording implies that the time stamps are captured at any level change.
There does not appear to be any way to only timestamp one edge of the
signal.

Reject requests which do not set both PTP_RISING_EDGE and PTP_FALLING_EDGE
when operating under PTP_STRICT_FLAGS mode via PTP_EXTTS_REQUEST2.

Fixes: 38970eac ("igb: support EXTTS on 82580/i354/i350")
Reviewed-by: Michal Swiatkowski <michal.swiatkowski@linux.intel.com>
Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/20250312-jk-net-fixes-supported-extts-flags-v2-1-ea930ba82459@intel.com


Signed-off-by: Paolo Abeni <pabeni@redhat.com>