Increases stack size for threads used in gt netsocket tcp test cases

Stack size is insufficient for debug profile
Stack size is insufficient for NUCLEO_F401RE+IDW01M1
Please see ARMmbed/wifi-x-nucleo-idw01m1#17

Author: Veijo Pesonen

TESTS/netsocket/tcp/tcp_tests.h

@@ -31,7 +31,7 @@ int split2half_rmng_tcp_test_time(); // [s]
 
 namespace tcp_global {
 static const int TESTS_TIMEOUT = 960;
-static const int TCP_OS_STACK_SIZE = 1024;
+static const int TCP_OS_STACK_SIZE = 2048;
 
 static const int RX_BUFF_SIZE = 1220;
 static const int TX_BUFF_SIZE = 1220;