6lowpan options (for ipv6)

Defines
#define	SICSLOWPAN_REASS_MAXAGE   20
	Timeout for packet reassembly at the 6lowpan layer (should be < 60s)
#define	SICSLOWPAN_CONF_COMPRESSION   0
	Do we compress the IP header or not (default: no)
#define	SICSLOWPAN_CONF_MAX_ADDR_CONTEXTS   1
	If we use IPHC compression, how many address contexts do we support.
#define	SICSLOWPAN_CONF_FRAG   0
	Do we support 6lowpan fragmentation.