ima: replace GFP_KERNEL with GFP_NOFS

While running fsstress tests on the NFSv4 mounted ext3 and ext4
filesystem, the following call trace was generated on the nfs
server machine.

Replace GFP_KERNEL with GFP_NOFS in ima_iint_insert() to avoid a
potential deadlock.

     =================================
    [ INFO: inconsistent lock state ]
    2.6.31-31.el6.x86_64 #1
    ---------------------------------
    inconsistent {RECLAIM_FS-ON-W} -> {IN-RECLAIM_FS-W} usage.
    kswapd2/75 [HC0[0]:SC0[0]:HE1:SE1] takes:
     (jbd2_handle){+.+.?.}, at: [<ffffffff811edd5e>] jbd2_journal_start+0xfe/0x13f
    {RECLAIM_FS-ON-W} state was registered at:
      [<ffffffff81091e40>] mark_held_locks+0x65/0x99
      [<ffffffff81091f31>] lockdep_trace_alloc+0xbd/0xf5
      [<ffffffff81126fdd>] kmem_cache_alloc+0x40/0x185
      [<ffffffff812344d7>] ima_iint_insert+0x3d/0xf1
      [<ffffffff812345b0>] ima_inode_alloc+0x25/0x44
      [<ffffffff811484ac>] inode_init_always+0xec/0x271
      [<ffffffff81148682>] alloc_inode+0x51/...