ice: add const qualifier to mac_addr parameter

The function ice_aq_manage_mac_write takes a pointer to a MAC address.
The parameter is not marked const, even though the function doesn't need
to modify it. This prevents passing a parameter that is already marked
const. Update the function prototype to take a const pointer, to allow
passing constant pointers to this function.

Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
Signed-off-by: Anirudh Venkataramanan <anirudh.venkataramanan@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>