iwlwifi: mvm: Set TX_CMD_FLG_PROT_REQUIRE correctly

Previously the protection flag wasn't set on multicast frames even if
the RA is unicast. Fix this by checking addr1 instead.

Signed-off-by: Andrei Otcheretianski <andrei.otcheretianski@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>