Put hostname option into DHCPDISCOVER/DHCPREQUEST if provided by system

If Haiku has the hostname set, inform DHCP server with corresponding
option in DHCPDISCOVER and DHCPREQUEST messages. That should simplify
accessing Haiku hosts by using it's hostname instead of raw addresses.

src/servers/net/DHCPClient.cpp

@@ -24,6 +24,7 @@
 #include <syslog.h>
 #include <sys/sockio.h>
 #include <sys/time.h>
+#include <unistd.h>
 
 #include <Debug.h>
 #include <Message.h>
@@ -541,6 +542,12 @@ DHCPClient::_Negotiate(dhcp_state state)
 	uint32 tries;
 	_ResetTimeout(socket, timeout, tries);
 
+	char hostName[MAXHOSTNAMELEN];
+	if (gethostname(hostName, MAXHOSTNAMELEN) == 0)
+		fHostName.SetTo(hostName, MAXHOSTNAMELEN);
+	else
+		fHostName.Truncate(0);
+
 	dhcp_message discover(DHCP_DISCOVER);
 	_PrepareMessage(discover, state);
 
@@ -842,12 +849,24 @@ DHCPClient::_PrepareMessage(dhcp_message& message, dhcp_state state)
 		case DHCP_DISCOVER:
 			next = message.PutOption(next, OPTION_REQUEST_PARAMETERS,
 				kRequestParameters, sizeof(kRequestParameters));
+
+			if (fHostName.Length() > 0) {
+				next = message.PutOption(next, OPTION_HOST_NAME,
+					reinterpret_cast<const uint8*>(fHostName.String()),
+					fHostName.Length());
+			}
 			break;
 
 		case DHCP_REQUEST:
 			next = message.PutOption(next, OPTION_REQUEST_PARAMETERS,
 				kRequestParameters, sizeof(kRequestParameters));
 
+			if (fHostName.Length() > 0) {
+				next = message.PutOption(next, OPTION_HOST_NAME,
+					reinterpret_cast<const uint8*>(fHostName.String()),
+					fHostName.Length());
+			}
+
 			if (state == REQUESTING) {
 				const sockaddr_in& server = (sockaddr_in&)fServer.SockAddr();
 				next = message.PutOption(next, OPTION_SERVER_ADDRESS,

src/servers/net/DHCPClient.h

@@ -66,6 +66,7 @@ private:
 			BMessage			fResolverConfiguration;
 			BMessageRunner*		fRunner;
 			uint8				fMAC[6];
+			BString				fHostName;
 			uint32				fTransactionID;
 			in_addr_t			fAssignedAddress;
 			BNetworkAddress		fServer;