fdtrack: add wrapper for socketpair.

Bug: https://issuetracker.google.com/154450436
Test: bionic-unit-tests
Change-Id: I8b25accf00dc01f6fab351f3ba612f6b0ff9d094
(cherry picked from commit b107eab5ef1d5946bd753cad0e8b178172d362df)
diff --git a/libc/SYSCALLS.TXT b/libc/SYSCALLS.TXT
index f235bc8..6142baf 100644
--- a/libc/SYSCALLS.TXT
+++ b/libc/SYSCALLS.TXT
@@ -243,7 +243,7 @@
 
 # sockets
 int           __socket:socket(int, int, int)              arm,lp64
-int           socketpair(int, int, int, int*)    arm,lp64
+int           __socketpair:socketpair(int, int, int, int*)    arm,lp64
 int           bind(int, struct sockaddr*, socklen_t)  arm,lp64
 int           __connect:connect(int, struct sockaddr*, socklen_t)   arm,lp64
 int           listen(int, int)                   arm,lp64
@@ -267,7 +267,7 @@
 int           listen:socketcall:4(int, int)                   x86
 int           getsockname:socketcall:6(int, struct sockaddr*, socklen_t*)  x86
 int           getpeername:socketcall:7(int, struct sockaddr*, socklen_t*)  x86
-int           socketpair:socketcall:8(int, int, int, int*)    x86
+int           __socketpair:socketcall:8(int, int, int, int*)    x86
 ssize_t       __sendto:socketcall:11(int, const void*, size_t, int, const struct sockaddr*, socklen_t)  x86
 ssize_t       recvfrom:socketcall:12(int, void*, size_t, unsigned int, struct sockaddr*, socklen_t*)  x86
 int           shutdown:socketcall:13(int, int)  x86