[msan] Replace AF_INET with AF_UNIX to avoid IPv4 vs IPv6 issues.

[vitalybuka]

Summary

This reverts commit 79cf16bf224d6ac9fb9e0356c5947ebc4fd6ff92.

test/msan/ioctl.cc

 // RUN: %clangxx_msan -O0 -g %s -o %t && %run %t
 // RUN: %clangxx_msan -O3 -g %s -o %t && %run %t
 
 #include <assert.h>
 #include <stdlib.h>
 #include <sys/ioctl.h>
 #include <sys/socket.h>
 #include <unistd.h>
 
 int main(int argc, char **argv) {
-  int fd = socket(AF_INET, SOCK_DGRAM, 0);
+  int fd = socket(AF_UNIX, SOCK_DGRAM, 0);
 
   unsigned int z;
   int res = ioctl(fd, FIOGETOWN, &z);
   assert(res == 0);
   close(fd);
   if (z)
     exit(0);
   return 0;
 }

test/msan/ioctl_custom.cc

 // RUN: %clangxx_msan -O0 -g %s -o %t && %run %t
 // RUN: %clangxx_msan -O3 -g %s -o %t && %run %t
 
 // RUN: %clangxx_msan -DPOSITIVE -O0 -g %s -o %t && not %run %t 2>&1 | FileCheck %s
 // RUN: %clangxx_msan -DPOSITIVE -O3 -g %s -o %t && not %run %t 2>&1 | FileCheck %s
 
 #include <assert.h>
 #include <stdlib.h>
 #include <net/if.h>
 #include <stdio.h>
 #include <string.h>
 #include <sys/ioctl.h>
 #include <sys/socket.h>
 #include <unistd.h>
 
 int main(int argc, char **argv) {
-  int fd = socket(AF_INET, SOCK_STREAM, 0);
+  int fd = socket(AF_UNIX, SOCK_STREAM, 0);
 
   struct ifreq ifreqs[20];
   struct ifconf ifc;
   ifc.ifc_ifcu.ifcu_req = ifreqs;
 #ifndef POSITIVE
   ifc.ifc_len = sizeof(ifreqs);
 #endif
   int res = ioctl(fd, SIOCGIFCONF, (void *)&ifc);
   // CHECK: Uninitialized bytes in ioctl{{.*}} at offset 0 inside [0x{{.*}}, 4)
   // CHECK: WARNING: MemorySanitizer: use-of-uninitialized-value
   // CHECK: #{{.*}} in main {{.*}}ioctl_custom.cc:[[@LINE-3]]
   assert(res == 0);
   for (int i = 0; i < ifc.ifc_len / sizeof(*ifc.ifc_ifcu.ifcu_req); ++i)
     printf("%d  %zu  %s\n", i, strlen(ifreqs[i].ifr_name), ifreqs[i].ifr_name);
   return 0;
 }