Consistently use types in e1000 driver code:

• Two struct members eee_disable are used in a function that expects an int *, so declare them int, not bool.
• igb_tx_ctx_setup() returns a boolean value, so declare it bool, not int.
• igb_header_split is passed to TUNABLE_INT, so delcare it int, not bool.
• igb_tso_setup() returns a bool, so declare it bool, not boolean_t.
• Do not re-define bool/true/false if the symbols already exist.

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