bnxt_en: Use PAGE_SIZE to init buffer when multi buffer XDP is not in use

Using BNXT_PAGE_MODE_BUF_SIZE + offset as buffer length value is not
sufficient when running single buffer XDP programs doing redirect
operations. The stack will complain on missing skb tail room. Fix it
by using PAGE_SIZE when calling xdp_init_buff() for single buffer
programs.

Fixes: b231c3f3

 ("bnxt: refactor bnxt_rx_xdp to separate xdp_init_buff/xdp_prepare_buff")
Reviewed-by: Somnath Kotur <somnath.kotur@broadcom.com>
Signed-off-by: Pavan Chebbi <pavan.chebbi@broadcom.com>
Signed-off-by: Michael Chan <michael.chan@broadcom.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>