Fix build with ToT libc++

packages/modules/Connectivity/staticlibs/netd/libnetdutils/InternetAddresses.cpp:140:31: error: use of undeclared identifier 'strtoul'
  140 |     unsigned long prefixlen = strtoul(prefixString, &endptr, 10);
      |

Test: Build with ToT libc++
Change-Id: I12e66d27897d11e6d6ace36312ef6b80b29d069e
1 file changed