Is there a way to disable Precision Time Protocol (PTP) on Intel I211 Gigabit w/igb driver?

The code to support HC on some intel cards has been added around 2011. The Intel® Ethernet Controller I211-AT supports hardware-based precision time synchronization. It is enabled because the module developers think of it in the following way: (source)

If a MAC has PTP features, then users will sure want it enabled.

Shorter: Your conclusion is correct. Still, you can do several things:

• Contact the module developers and show your use-case. Convince them that there are good reasons to disable a functionality even if it is generally considered as wanted and turned on by default.
• Recompile the module with the HC removed.
• Try to use the Realtek NIC instead.
• Try to configure gpsd to ignore devices as /dev/pps0 or /dev/ptp0 - according to the documentation is should be possible:

To tell the daemon that a device has been disconnected and is no longer available, send a minus sign ('-') followed by the device name followed by LF or CR-LF. Thus, to remove /dev/foo from the search list, send "-/dev/foo\n".

This should also work automated, by modifying the files under /etc/gpsd/device-hook.