udhcp: abort if we see unknown option, and show valid options if so

function                                             old     new   delta
udhcp_option_idx                                       -      77     +77
udhcp_str2optset                                     366     351     -15
udhcpc_main                                         2845    2801     -44
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(add/remove: 1/0 grow/shrink: 0/2 up/down: 77/-59)             Total: 18 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
3 files changed