LU-12923 ptlrpc: Use BUILD_BUG_ON() for pack_generic.c

LU-12923 ptlrpc: Use BUILD_BUG_ON() for pack_generic.c

This patch replaces all CLASSERT() with kernel defined
BUILD_BUG_ON() for file lustre/ptlrpc/pack_generic.c

This patch also fixes few space/tab issues reported
by checkpatch

Test-Parameters: trivial
Signed-off-by: Arshad Hussain <arshad.super@gmail.com>
Change-Id: I1903f9faad8b1dec7c550a6b653dcb899aaa0b98
Reviewed-on: https://review.whamcloud.com/36649
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Shaun Tancheff <stancheff@cray.com>
Reviewed-by: Petros Koutoupis <pkoutoupis@cray.com>
Reviewed-by: James Simmons <jsimmons@infradead.org>
Reviewed-by: Oleg Drokin <green@whamcloud.com>