Make SPI_ETHERNET_SETTINGS and MAX_SOCK_NUM configurable at the project level

Closes arduino-libraries#267

Author: joeyparrish

src/Ethernet.h

@@ -33,10 +33,12 @@
 // up to 4 sockets.  W5200 & W5500 can have up to 8 sockets.  Several bytes
 // of RAM are used for each socket.  Reducing the maximum can save RAM, but
 // you are limited to fewer simultaneous connections.
-#if defined(RAMEND) && defined(RAMSTART) && ((RAMEND - RAMSTART) <= 2048)
-#define MAX_SOCK_NUM 4
-#else
-#define MAX_SOCK_NUM 8
+#if !defined(MAX_SOCK_NUM)
+# if defined(RAMEND) && defined(RAMSTART) && ((RAMEND - RAMSTART) <= 2048)
+#  define MAX_SOCK_NUM 4
+# else
+#  define MAX_SOCK_NUM 8
+# endif
 #endif
 
 // By default, each socket uses 2K buffers inside the WIZnet chip.  If

src/utility/w5100.h

@@ -18,7 +18,9 @@
 #include <SPI.h>
 
 // Safe for all chips
-#define SPI_ETHERNET_SETTINGS SPISettings(14000000, MSBFIRST, SPI_MODE0)
+#if !defined(SPI_ETHERNET_SETTINGS)
+# define SPI_ETHERNET_SETTINGS SPISettings(14000000, MSBFIRST, SPI_MODE0)
+#endif
 
 // Safe for W5200 and W5500, but too fast for W5100
 // Uncomment this if you know you'll never need W5100 support.