parse: change offset type

to fit with mnl_nlmsg_get_payload_offset()
seq, portid: change type to uint32_t

following struct nlmsghdr
Merge branch 'master' of https://github.com/chamaken/libmnl
examples: use mnl_nlmsg_get_payload()

not increment (nlmsghdr) pointer
Merge branch 'master' into mmap2