Fix the definedness handling of the last argument of sys_socketpair.

Fix the definedness handling of the last argument of sys_socketpair.
The last argument is really a pointer to an array of two ints and so
we need to say it is an int* and not an int [2].  This just happens to
work on amd64-linux because sizeof(int [2]) == 8 == sizeof(int*).  On
arm-linux it duly craps out w/ an assertion because sizeof(int [2]) !=
sizeof(UWord).

git-svn-id: svn://svn.valgrind.org/valgrind/trunk@11083