Fix dependency for IFUPDOWN_UDHCPC_CMD_OPTIONS

Fix dependency for IFUPDOWN_UDHCPC_CMD_OPTIONS

Commit a8c696bf09d8151323f6e99348c4bc8989f829c8 makes ifup and ifdown
individually selectable, but forgets to update the dependency to
IFUPDOWN_UDHCPC_CMD_OPTIONS, so it is not selectable anymore.

This patch fixes the dependency by checking for IFUP or IFDOWN, instead
of the obsolete IFUPDOWN.

Also, it drops dependency on UDHCPC: udhcpc on the target system
does not have to come from the _same_ binary.

Signed-off-by: Jörg Krause <joerg.krause@embedded.rocks>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>