Use blocking sockets when testing raw IP sockets

The original code instantiated the raw IP sockets with NON_BLOCKING,
which caused problems in the PingSuccessfully test case. That case sends
and expects to immediately receive an ICMPv6 Echo Request/Reply. On
Fuchsia, the Loopback devices tx/rx queues are decoupled, so it's
possible for the test to call `recvmsg` before the packet has been
delivered to the socket (resulting in EAGAIN). By using a blocking
socket, the test will wait until `recvmsg` no longer returns EAGAIN.

PiperOrigin-RevId: 641989486

Author: Jeff-A-Martin

test/syscalls/linux/raw_socket_icmp.cc

@@ -592,8 +592,7 @@ class RawSocketICMPv6Test : public Test {
   void SetUp() override {
     SKIP_IF(!ASSERT_NO_ERRNO_AND_VALUE(HaveRawIPSocketCapability()));
 
-    fd_ = ASSERT_NO_ERRNO_AND_VALUE(
-        Socket(AF_INET6, SOCK_RAW | SOCK_NONBLOCK, IPPROTO_ICMPV6));
+    fd_ = ASSERT_NO_ERRNO_AND_VALUE(Socket(AF_INET6, SOCK_RAW, IPPROTO_ICMPV6));
   }
 
   void TearDown() override {