enic: change sprintf() to snprintf()

These are copying data into 16 char arrays.  They all specify that the
first string can't be more than 11 characters but once you add on the
"-rx-" and the NUL character there isn't space for the %d.

The first string is probably never going to be 11 characters, but if it
is then let's truncate the string instead of corrupting memory.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>