kernel: pf_ring: better define sa_data size

[Ansuel]

pfring_mod_bind() needs to specify the interface name using struct sockaddr that is defined as

struct sockaddr { ushort sa_family; char sa_data[14]; };

so the total interface name length is 13 chars (plus \0 trailer).

Since sa_data size is arbitrary, define a more precise size for PF_RING socket use.

This fix some compilation error with fortify string and makes the array handling more deterministic.

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• [x] I have updated the documentation (in doc/) to reflect the changes made (if applicable)

[cardigliano]

Where is RING_SA_DATA_LEN defined when RING_USE_SOCKADDR_LL is defined?

[Ansuel]

@cardigliano sorry I didn't notice that function was also used by the LL variant. I tested this on previous version where the ifdef wasn't present. Should be good now.