udhcp: add 100 and 101 dhcp options for ipv4

udhcp: add 100 and 101 dhcp options for ipv4

Support for the IEEE timezone string and timezone database strings (100
and 101 options respectively) is added for ipv4, conforming to RFC-4833.

The two options are passed to hook scripts in the variables tzstr and
tzdbstr.

function                                             old     new   delta
dhcp_option_strings                                  280     294     +14
dhcp_optflags                                         76      80      +4
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(add/remove: 0/0 grow/shrink: 2/0 up/down: 18/0)               Total: 18 bytes

Signed-off-by: Antoine Girard-Vallée <antoine.girard-vallee@savoirfairelinux.com>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>