ACS: Update documentation of external ACS results event parameters

ACS: Update documentation of external ACS results event parameters

Update the documentation with values to be sent for seg0 and seg1 fields
in external ACS result event for 20 MHz, 40 MHz, 80 MHz, 160 MHz, and
80+80 MHz channels. These values match the changes done to definitions
of seg0 and seg1 fields in the IEEE 802.11 standard.

This vendor command had not previously been documented in this level of
detail and had not actually been used for the only case that could have
two different interpretation (160 MHz) based on which version of IEEE
802.11 standard is used.

Signed-off-by: Jouni Malinen <jouni@codeaurora.org>