[nrf fromlist] drivers: nrfwifi: Fix CSUM support

With introduction of Raw modes, nRF70 driver now advertises get_c
onfig OP, but doesn't implement all types.

This causes problems two-fold with checksum calculations:
  1. The "config" isn't uninitialized, so, every call returns differnet
     values. So, for UDP header checksum would be done and
     pkt->chksumdone would be set. But for IPv4 header checksum might be
     skipped.
  2. Even if we initialize to zero, then network stack gets all zeros
     and calculates checksum by itself rendering offload moot.

There is another problem in zephyrproject-rtos#1, as there is only single flag for pkt for
all checksum, nRF70 driver sees this and tells UMAC to skip checksum for
the entire packet. The design isn't coherent, and should be converted to
communicate per-type checksum status (some are filled by network stack
and some HW).

But as nRF70 support all checksum offloads, advertise all types for both
RX and TX.

Upstream PR #: 80882

Signed-off-by: Chaitanya Tata <Chaitanya.Tata@nordicsemi.no>
(cherry picked from commit 3017425)

drivers/wifi/nrfwifi/src/net_if.c

@@ -980,10 +980,23 @@ int nrf_wifi_if_get_config_zep(const struct device *dev,
 		goto unlock;
 	}
 
+	memset(config, 0, sizeof(struct ethernet_config));
+
 	if (type == ETHERNET_CONFIG_TYPE_TXINJECTION_MODE) {
 		config->txinjection_mode =
 			def_dev_ctx->vif_ctx[vif_ctx_zep->vif_idx]->txinjection_mode;
 	}
+#ifdef CONFIG_NRF70_TCP_IP_CHECKSUM_OFFLOAD
+	if (type  == ETHERNET_CONFIG_TYPE_TX_CHECKSUM_SUPPORT ||
+	    type == ETHERNET_CONFIG_TYPE_RX_CHECKSUM_SUPPORT) {
+		config->chksum_support = ETHERNET_CHECKSUM_SUPPORT_IPV4_HEADER |
+					 ETHERNET_CHECKSUM_SUPPORT_IPV4_ICMP |
+					 ETHERNET_CHECKSUM_SUPPORT_IPV6_HEADER |
+					 ETHERNET_CHECKSUM_SUPPORT_IPV6_ICMP |
+					 ETHERNET_CHECKSUM_SUPPORT_TCP |
+					 ETHERNET_CHECKSUM_SUPPORT_UDP;
+	}
+#endif
 	ret = 0;
 unlock:
 	k_mutex_unlock(&vif_ctx_zep->vif_lock);