bnxt_en: Add bnxt_set_max_func_irqs().

bnxt_en: Add bnxt_set_max_func_irqs().

Orabug: 24567991

By refactoring existing code into this new function.  The new function
will be used in subsequent patches.

v2: Fixed compile warning when CONFIG_BNXT_SRIOV is not set.

Signed-off-by: Michael Chan <michael.chan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
(cherry picked from commit 33c2657eb688a063ab9cbe11fd4d18c93c7945e1)
Signed-off-by: Brian Maly <brian.maly@oracle.com>
Signed-off-by: Dhaval Giani <dhaval.giani@oracle.com>