Seperatig string literal from macro

From C++11 and beyond string literals must be seperated by space
so that they are recongizable as seperate tokens.

Context macro in PPPCellularInterface (CTX) has been causing issues
as it was not augmented with a space from a nearby string literal.

Author: Hasnain Virk

features/netsocket/cellular/generic_modem_driver/PPPCellularInterface.cpp

@@ -141,7 +141,7 @@ static void CMT_URC(ATCmdParser *at)
 
 static bool set_atd(ATCmdParser *at)
 {
-    bool success = at->send("ATD*99***" CTX"#") && at->recv("CONNECT");
+    bool success = at->send("ATD*99***" CTX "#") && at->recv("CONNECT");
 
     return success;
 }
@@ -469,7 +469,7 @@ nsapi_error_t PPPCellularInterface::setup_context_and_credentials()
 #endif
     success = _at->send("AT"
                           "+FCLASS=0;" // set to connection (ATD) to data mode
-                          "+CGDCONT=" CTX",\"%s\",\"%s%s\"",
+                          "+CGDCONT=" CTX ",\"%s\",\"%s%s\"",
                           pdp_type, auth, _apn
                          )
                    && _at->recv("OK");