Description:
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In network/socket programming in Linux there are situations when one needs to 
bind the socket to a specific interface. This is especially important when 
dealaing with broadcasts. Linux has SO_BINDTODEVICE to do this.
But currently it is impossible to use this option with PHP as any unknown 
options value will get translated to long and only then passed to setsockopt.

There are two ways to address this issue.

Change the default handler so, that if the argument is string, this is actually 
passed to setsockopt. This not only solves this issue, but also opens 
impossibles for future options with funky format where pack() may be abused to 
get them working without changes to the extension code.

But as this might break BC, there are two other approaches:
1. Just add a case statement specifically for SO_BINDTODEVICE
2. Add some sort of flag to the function parameters (either a bit in the options 
argument, or something else) that requests this special "raw" processing of the 
argument value.

It would make sense to have the socket_get_option counterpart also implemented. 
Not provided in the patch.