enic: move struct definition from .c to .h file

Some of the structure definitions are in .c file to make them private to
that file. This patch moves the struct definition to .h file, So that their
definitions are accessible from other files.

Signed-off-by: Govindarajulu Varadarajan <_govind@gmx.com>
Signed-off-by: David S. Miller <davem@davemloft.net>