net/bnxt: fix dynamic VNIC count

net/bnxt: fix dynamic VNIC count

Ensure that the current count of in-use VNICs is decremented
when a VNIC is freed. Don't attempt VNIC allocation when the
maximum supported number of VNICs is currently allocated.

Fixes: 49d0709b257f ("net/bnxt: delete and flush L2 filters cleanly")
Fixes: d24610f7bfda ("net/bnxt: allow flow creation when RSS is enabled")
Cc: stable@dpdk.org
Signed-off-by: Lance Richardson <lance.richardson@broadcom.com>
Reviewed-by: Ajit Khaparde <ajit.khaparde@broadcom.com>
Reported-by: Stephen Hemminger <sthemmin@microsoft.com>