ipconfig: Protect ic_addrservaddr with IPCONFIG_DYNAMIC.

>> net/ipv4/ipconfig.c:130:15: warning: 'ic_addrservaddr' defined but not used [-Wunused-variable]
    static __be32 ic_addrservaddr = NONE; /* IP Address of the IP addresses'server */

Reported-by: kbuild test robot <fengguang.wu@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/ipconfig.c

@@ -127,7 +127,9 @@ __be32 ic_myaddr = NONE;		/* My IP address */
 static __be32 ic_netmask = NONE;	/* Netmask for local subnet */
 __be32 ic_gateway = NONE;	/* Gateway IP address */
 
+#ifdef IPCONFIG_DYNAMIC
 static __be32 ic_addrservaddr = NONE;	/* IP Address of the IP addresses'server */
+#endif
 
 __be32 ic_servaddr = NONE;	/* Boot server IP address */