[posix] improve the logging in netif (#10362)

This commit improves the logging of `posix/platform/netif.cpp` in
following ways:

- Fix the false warning log when OT stack adds a unicast address.
  1. When OT adds an address, it will add an address on host netif.
  2. Then it causes a netlink `RTM_NEWADDR` event.
  3. It assumes the newly added address is added by the host, so tries
     to add the unicast address to OT again by
     `otIp6AddUnicastAddress`.
  4. `otIp6AddUnicastAddress` returns 'invalid arguments' error so it
     will log `Failed to process event...`.

- Improve the logging of `AddRoute` and `DeleteRoute`. Previously they
  silently sent out the requests so we don't know what the allocated
  netlink sequence numbers were used for.

src/posix/platform/netif.cpp

@@ -652,7 +652,8 @@ template <size_t N> otError AddRoute(const uint8_t (&aAddress)[N], uint8_t aPref
         char            buf[kBufSize];
     } req{};
     unsigned int netifIdx = otSysGetThreadNetifIndex();
-    otError      error    = OT_ERROR_NONE;
+    char         addrStrBuf[INET6_ADDRSTRLEN];
+    otError      error = OT_ERROR_NONE;
 
     static_assert(N == sizeof(in6_addr) || N == sizeof(in_addr), "aAddress should be 4 octets or 16 octets");
 
@@ -680,11 +681,18 @@ template <size_t N> otError AddRoute(const uint8_t (&aAddress)[N], uint8_t aPref
     AddRtAttrUint32(&req.header, sizeof(req), RTA_PRIORITY, aPriority);
     AddRtAttrUint32(&req.header, sizeof(req), RTA_OIF, netifIdx);
 
+    inet_ntop(req.msg.rtm_family, aAddress, addrStrBuf, sizeof(addrStrBuf));
+
     if (send(sNetlinkFd, &req, sizeof(req), 0) < 0)
     {
+        LogInfo("Failed to send request#%u to add route %s/%u", sNetlinkSequence, addrStrBuf, aPrefixLen);
         VerifyOrExit(errno == EAGAIN || errno == EINTR || errno == EWOULDBLOCK, error = OT_ERROR_BUSY);
         DieNow(OT_EXIT_ERROR_ERRNO);
     }
+    else
+    {
+        LogInfo("Sent request#%u to add route %s/%u", sNetlinkSequence, addrStrBuf, aPrefixLen);
+    }
 exit:
     return error;
 }
@@ -699,7 +707,8 @@ template <size_t N> otError DeleteRoute(const uint8_t (&aAddress)[N], uint8_t aP
         char            buf[kBufSize];
     } req{};
     unsigned int netifIdx = otSysGetThreadNetifIndex();
-    otError      error    = OT_ERROR_NONE;
+    char         addrStrBuf[INET6_ADDRSTRLEN];
+    otError      error = OT_ERROR_NONE;
 
     static_assert(N == sizeof(in6_addr) || N == sizeof(in_addr), "aAddress should be 4 octets or 16 octets");
 
@@ -726,11 +735,18 @@ template <size_t N> otError DeleteRoute(const uint8_t (&aAddress)[N], uint8_t aP
     AddRtAttr(reinterpret_cast<nlmsghdr *>(&req), sizeof(req), RTA_DST, &aAddress, sizeof(aAddress));
     AddRtAttrUint32(&req.header, sizeof(req), RTA_OIF, netifIdx);
 
+    inet_ntop(req.msg.rtm_family, aAddress, addrStrBuf, sizeof(addrStrBuf));
+
     if (send(sNetlinkFd, &req, sizeof(req), 0) < 0)
     {
+        LogInfo("Failed to send request#%u to delete route %s/%u", sNetlinkSequence, addrStrBuf, aPrefixLen);
         VerifyOrExit(errno == EAGAIN || errno == EINTR || errno == EWOULDBLOCK, error = OT_ERROR_BUSY);
         DieNow(OT_EXIT_ERROR_ERRNO);
     }
+    else
+    {
+        LogInfo("Sent request#%u to delete route %s/%u", sNetlinkSequence, addrStrBuf, aPrefixLen);
+    }
 
 exit:
     return error;
@@ -1340,6 +1356,7 @@ static void processNetifAddrEvent(otInstance *aInstance, struct nlmsghdr *aNetli
                     netAddr.mPrefixLength = ifaddr->ifa_prefixlen;
 
                     error = otIp6AddUnicastAddress(aInstance, &netAddr);
+                    error = (error == OT_ERROR_INVALID_ARGS) ? OT_ERROR_NONE : error;
                 }
                 else
                 {