RDMA/bnxt_re: add DCB dependency

When CONFIG_DCB is disabled, we get a link error:

drivers/infiniband/built-in.o: In function `bnxt_re_setup_qos':
trace.c:(.text+0x155774): undefined reference to `dcb_ieee_getapp_mask'
trace.c:(.text+0x155774): relocation truncated to fit: R_AARCH64_CALL26 against undefined symbol `dcb_ieee_getapp_mask'
trace.c:(.text+0x155794): undefined reference to `dcb_ieee_getapp_mask'
trace.c:(.text+0x155794): relocation truncated to fit: R_AARCH64_CALL26 against undefined symbol `dcb_ieee_getapp_mask'

Like the other drivers that use this function, a Kconfig dependency is
the correct fix.
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Doug Ledford <dledford@redhat.com>

drivers/infiniband/hw/bnxt_re/Kconfig

 config INFINIBAND_BNXT_RE
     tristate "Broadcom Netxtreme HCA support"
-    depends on ETHERNET && NETDEVICES && PCI && INET
+    depends on ETHERNET && NETDEVICES && PCI && INET && DCB
     select NET_VENDOR_BROADCOM
     select BNXT
     ---help---