- Added the NIC_PFILTER configuration option in Kconfig to decide which filter rules will be used.
	- Updated the dev/ep_pfilter.c file by using the CONFIG_NIC_PFILTER macro. This is done because packet filter does
	not work correctly if we write all rules in the CONFIG_ETHERBONE section.
	- We do not use the DROP instruction because all other packets go to NIC core.

Notes:

	- The filter rules to the wr-nic do not have the DROP instruction because all traffic
	does not go to the LM32/Etherbone is re-direct to the NIC by default.

	- The NIC_PFILTER configuration option depends on ETHERBONE one.

	- Magic number of Etherbone packets is not checked due to the number of rules. (The packet filter is not able to classify correctly)