How do I display information about an interface controller?

Use the nicinfo command:

/usr/sbin/nicinfo device
Note: If you aren't logged in as root, you have to specify the full path to nicinfo.

This utility displays information about the given network interface connection, or /dev/io-net/en0 if you don't specify one. The information includes the number of packets transmitted and received, collisions, and other errors, as follows:

3COM (90xC) 10BASE-T/100BASE-TX Ethernet Controller
  Physical Node ID ................. 000103 E8433F
  Current Physical Node ID ......... 000103 E8433F
  Media Rate ....................... 10.00 Mb/s half-duplex UTP
  MTU .............................. 1514
  Lan .............................. 0
  I/O Port Range ................... 0xA800 -> 0xA87F
  Hardware Interrupt ............... 0x7
  Promiscuous ...................... Disabled
  Multicast ........................ Enabled

  Total Packets Txd OK ............. 1585370
  Total Packets Txd Bad ............ 9
  Total Packets Rxd OK ............. 11492102
  Total Rx Errors .................. 0

  Total Bytes Txd .................. 102023380
  Total Bytes Rxd .................. 2252658488

  Tx Collision Errors .............. 39598
  Tx Collisions Errors (aborted) ... 0
  Carrier Sense Lost on Tx ......... 0
  FIFO Underruns During Tx ......... 0
  Tx deferred ...................... 99673
  Out of Window Collisions ......... 0
  FIFO Overruns During Rx .......... 0
  Alignment errors ................. 0
  CRC errors ....................... 0.