[PKTGEN]: Removes thread_{un,}lock() macros.

As suggested by Arnaldo, this patch replaces the
thread_lock()/thread_unlock() by directly calls to
mutex_lock()/mutex_unlock().

This change makes the code a bit more readable, and the direct calls
are used everywhere in the kernel.

Signed-off-by: Luiz Capitulino <lcapitulino@mandriva.com.br>
Signed-off-by: David S. Miller <davem@davemloft.net>