Add manual pages for kether_ntoa and kether_aton functions.
Add a manpage for hexncpy function.

Also fix .Dd in kether_ntoa(9).
doc - Add a note about %D removal in porting_drivers.txt document.
em/emx: Clear bit 28 of TARC1 for 82571/82572/es2lan

Clearing bit 28 of TARC1 is done in HAL's device initialization, however,
it happens before the MULR bit is turned on in TX unit initialization;
MULR is not necessarily on by default, since its value is loaded from
EEPROM according to the datasheet.