Consistently use types in ixgbe driver code:

• {ixgbe,ixv}_header_split is passed to TUNABLE_INT, so delcare it int, not bool.
• {ixgbe,ixv}_tx_ctx_setup() returns a boolean value, so declare it bool, not int.
• {ixgbe,ixv}_tso_setup() returns a bool, so declare it bool, not boolean_t.
• {ixgbe,ixv}_txeof() returns a bool, so declare it bool, not boolean_t.
• Do not re-define bool if the symbol already exists.

MFC after: 2 weeks
Sponsored by: Isilon Systems, LLC