netlink: uapi: use hex numbers for NLM_F_* flags

It's rather confusing that the netlink message flags are
numbered 1, 2, 4, 8, 16, 32, <unused>, 0x100. Make that
more understandable by numbering the lower ones with hex
constants as well.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>