Making IFQ_MAXLEN tunable

Hi,

Many network drivers in the FreeBSD kernel use the IFQ_MAXLEN value to 
set length of the outgoing packets queue. The default value for that 
parameter is only 50, which is pretty low especially for the cases when 
the system handles lot of small packets and can cause ENOBUFS in 
applications under the load. The following patch makes IFQ_MAXLEN a 
tunable. I am also tempted to bump the default value for IFQ_MAXLEN 
10-fold, but would like to hear what do people think about it first.

http://sobomax.sippysoft.com/IFQ_MAXLEN.diff

-Maxim