net: tulip: Remove private "strncmp"

The comment says that the built-in strncmp didn't work. That is not
surprising, as apparently "str" semantics are not really what is
wanted (hint: de4x5_strncmp only stops when two different bytes are
encountered or the end is reached; not if either byte happens to be
0). de4x5_strncmp is actually a memcmp (except for the signature and
that bytes are not necessarily treated as unsigned char); since only
the boolean value of the result is used we can just replace
de4x5_strncmp with memcmp.

Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Acked-by: Grant Grundler <grundler@parisc-linux.org>
Signed-off-by: David S. Miller <davem@davemloft.net>