b=19069 save nid string into buffer before creating dir

b=19069 save nid string into buffer before creating dir

in lprocfs_exp_setup, save the nid string gotten from
libcfs_nid2str into a temporary buffer before calling
lprocfs_register to create proc directory, then to
avoid the race on the internal nid string buffer.

i=johann@sun.com
i=zhen.liang@sun.com