gcoap: Update unit tests for rebase on sock

tests/unittests/tests-gcoap/Makefile.include

@@ -1,9 +1,8 @@
 USEPKG += nanocoap
-# Required by nanocoap to compile nanocoap_sock.
-USEMODULE += gnrc_sock_udp
 
 # Specify the mandatory networking modules
 USEMODULE += gcoap
+USEMODULE += gnrc_sock_udp
 USEMODULE += gnrc_ipv6
 
 USEMODULE += random