make: introduce *_default pseudo-modules

make: actually disable a DISABLED_MODULE

periph_pwm: Return actual frequency (like the docs say)

boards/pba-d-01-kw2x: add board to m4 travis build group

Fixes #2971

ng_ndp: initial import of address resolution

ng_icmpv6_echo: fix setting of ID field

ipv6_netif: prepare for NDP

drivers/isl29125: fix group description

sys/net/network_layer/sixlowpan/ip.c: remove unnecessary address-of-operator

sys/.../icmp.c: fix wrong ndp_add_prefix_info parameter

oonf_api: update pkg url

sys/.../icmp.c: fix prefix search

sys/.../ip.c: fix ipv6_net_if_get_best_src_addr

ng_icmpv6: pre-set checksum field to 0 for sending

drone: added Drone file

sys/compat/hwtimer: fix unused fcpu warning

This patch fixes ipv6_net_if_get_best_src_addr,
the function seems not to be finished.
The patch also adds a filter for the prefixes,
it is necessary because the prefixes are stored
in the same list as the addresses.

Replace equal operator inside ndp_prefix_info_search by not equal.
Otherwise, the existing prefix can not be found.

Inside the function recv_rtr_adv, ndp_add_prefix_info was called
with the wrong parameter.

ng_ipv6/netif: fix debug in _add_addr_to_entry()