ss: Allow excluding a socket table from being queried

ss: Allow excluding a socket table from being queried

The original problem was that a simple call to 'ss' leads to loading of
sctp_diag kernel module which might not be desired. While searching for
a workaround, it became clear how inconvenient it is to exclude a single
socket table from being queried.

This patch allows to prefix an item passed to '-A' parameter with an
exclamation mark to inverse its meaning.

Signed-off-by: Phil Sutter <phil@nwl.cc>