iavf: Fix race condition between iavf_shutdown and iavf_remove

Fix a deadlock introduced by commit
97457801 ("iavf: Add waiting so the port is initialized in remove")
due to race condition between iavf_shutdown and iavf_remove, where
iavf_remove stucks forever in while loop since iavf_shutdown already
set __IAVF_REMOVE adapter state.

Fix this by checking if the __IAVF_IN_REMOVE_TASK has already been
set and return if so.

Fixes: 97457801

 ("iavf: Add waiting so the port is initialized in remove")
Signed-off-by: Slawomir Laba <slawomirx.laba@intel.com>
Signed-off-by: Mateusz Palczewski <mateusz.palczewski@intel.com>
Tested-by: Marek Szlosek <marek.szlosek@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>