bnx2: Allow user-specified multiple advertisement speed values.

Remove unnecessary code that works around older versions of ethtool
that can pass down invalid advertisement speed values.  This old
code prevents the user from specifying multiple advertisement values.
The new code uses simple masking to mask out invalid advertisment bits.

Reported-by: Vlad Yasevich <vladislav.yasevich@hp.com>
Signed-off-by: Michael Chan <mchan@broadcom.com>
Signed-off-by: Benjamin Li <benli@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>