s3: Added SMB_VFS_INIT_SEARCH_OP to initialize data at the beginning of SMB search...

s3: Added SMB_VFS_INIT_SEARCH_OP to initialize data at the beginning of SMB search requests.

By default this VFS call is a NOOP, but the onefs vfs module takes advantage
of it to initialize direntry search caches at the beginning of each
TRANS2_FIND_FIRST, TRANS2_FIND_NEXT, SMBffirst, SMBsearch, and SMBunique