validation: pool: fix uarea init test for external pools

The max payload of single segmented packets in external
pools depends on the odp_header_size, app_header_size,
max_headroom_size and odp_trailer_size.

Take all these into consideration when doing packet alloc
from external pools so that allocations don't fail.

Signed-off-by: Ashwin Sekhar T K <asekhar@marvell.com>

test/validation/api/pool/pool.c

@@ -2050,9 +2050,15 @@ static void test_packet_pool_ext_uarea_init(void)
 	CU_ASSERT(data.count == num);
 
 	for (i = 0; i < num; i++) {
+		uint32_t max_payload;
+
 		CU_ASSERT(data.mark[i] == 1);
 
-		pkts[i] = odp_packet_alloc(pool, (param.pkt.buf_size - param.pkt.headroom) / 2);
+		max_payload = param.pkt.buf_size;
+		max_payload -= capa.pkt.odp_header_size + param.pkt.app_header_size;
+		max_payload -= capa.pkt.odp_trailer_size;
+		max_payload -= capa.pkt.max_headroom_size;
+		pkts[i] = odp_packet_alloc(pool, max_payload);
 
 		CU_ASSERT(pkts[i] != ODP_PACKET_INVALID);