net: do not check if an unsigned variabe is less than 0
net: do not check if an unsigned variabe is less than 0

otherwise GCC complains like:

src/seastar/src/net/posix-stack.cc:291:25: warning: comparison of
unsigned expression in ‘< 0’ is always false [-Wtype-limits]
  291 |         if ((prefix_len < 0 || prefix_len > 128)  ||
(src_prefix_len != 0)
      |              ~~~~~~~~~~~^~~

Signed-off-by: Kefu Chai <a4b264ee037c625052534d60505bfd0db4776ac4@redhat.com>
Message-Id: <f8098a7bd4c34fd836918db17ccd8766c8b2e2d9@gmail.com>

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