Move include/nuttx/net/uip/uip-arch.h to include/nuttx/net/arp.h; rename all uip_arp_ functions to arp_

Move include/nuttx/net/uip/uip-arch.h to include/nuttx/net/arp.h; rename all uip_arp_ functions to arp_

snprintf():  If size is zero, then snprintf() should return the size of the required buffer without writing anyting.  From Sami Pelkonen

snprintf():  If size is zero, then snprintf() should return the size of the required buffer without writing anyting.  From Sami Pelkonen

STM32 RTC: Add retry to initialization logic.  Sometime RTC initialization takes longer.  From dlsitzer.

STM32 RTC: Add retry to initialization logic.  Sometime RTC initialization takes longer.  From dlsitzer.

Configuration has CC3000_SPI_MODE settings but source uses CONFIG_CC3000_SPIMODE. From Jussi Kivilinna

Make sure that all references to up_prioritize_irq() are conditioned on CONFIG_ARCH_IRQPRIO.  Noted by Make Smith

Make sure that all references to up_prioritize_irq() are conditioned on CONFIG_ARCH_IRQPRIO.  Noted by Make Smith

Add an alternate STM32 I2C driver that works around errata in the F103 chip (and maybe others).  From Patrizio Simona