udhcpc: add -o "do not request options by default" switch

udhcpc: add -o "do not request options by default" switch
(by L. Gabriel Somlo <somlo AT cmu.edu>)

function                                             old     new   delta
udhcpc_main                                         2513    2554     +41
static.udhcpc_longopts                               226     247     +21
add_param_req_option                                 119     132     +13
packed_usage                                       23952   23964     +12
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(add/remove: 0/0 grow/shrink: 4/0 up/down: 87/0)               Total: 87 bytes