misc: Use g_assert_not_reached for code which is expected to be unreachable

The macro g_assert_not_reached is a better self documenting replacement
for assert(0) or assert(false).

Signed-off-by: Stefan Weil <sw@weilnetz.de>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>

net/eth.c

@@ -73,7 +73,7 @@ eth_get_gso_type(uint16_t l3_proto, uint8_t *l3_hdr, uint8_t l4proto)
     }
 
     /* Unsupported offload */
-    assert(false);
+    g_assert_not_reached();
 
     return VIRTIO_NET_HDR_GSO_NONE | ecn_state;
 }