be2net: Fix number of VLANs supported in UMC mode for BE3-R.

In BE3-R, when UMC is enabled, the number of VLANs that can be added
to the interface is reduced to 15.

Signed-off-by: Ajit Khaparde <ajit.khaparde@emulex.com>
Signed-off-by: David S. Miller <davem@davemloft.net>