force-dhcp can be used to retrieve a URL to the dot-config, which is downloaded
during boot.
try-dhcp the same as above but don't complain about unsuccessful receive of the
URL via DHCP to SNMP.

Update:
--MIB - add tryDhcp and forceDhcp to the wrsConfigSource object; add
        dhcpError to the wrsBootConfigStatus object
--SNMPd - same as the above; don't error in wrsBootConfigStatus when tryDhcp
          fails
--dot-config's script - support new dot-config sources
--Kconfig - support new dot-config sources
--wrs_failures
--wrs-user-manual
--wrs_release_defconfig - add new items
--create new script for udhcpc to save "filename" configuration field retrieved
  from DHCP server; it contains the URL to the dot-config to be downloaded.

Signed-off-by: Adam Wujek <adam.wujek@cern.ch>