bnxt_en: refactor bnxt_alloc_rx_rings() to call bnxt_alloc_rx_agg_bmap()

Refactor bnxt_alloc_rx_rings() to call bnxt_alloc_rx_agg_bmap() for
allocating rx_agg_bmap.

Reviewed-by: Somnath Kotur <somnath.kotur@broadcom.com>
Signed-off-by: David Wei <dw@davidwei.uk>
Reviewed-by: Michael Chan <michael.chan@broadcom.com>
Link: https://patch.msgid.link/20241204041022.56512-3-dw@davidwei.uk


Signed-off-by: Jakub Kicinski <kuba@kernel.org>