[DCCP]: Introduce DCCP_{BUG{_ON},CRIT} macros, use enum:8 for the ccid3 states

[DCCP]: Introduce DCCP_{BUG{_ON},CRIT} macros, use enum:8 for the ccid3 states

This patch tackles the following problem:
       * the ccid3_hc_{t,r}x_sock define ccid3hc{t,r}x_state as `u8', but
         in reality there can only be a few, pre-defined enum names
       * this necessitates addiditional checking for unexpected values
         which would otherwise be caught by the compiler

Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk>
Signed-off-by: Arnaldo Carvalho de Melo <acme@mandriva.com>