base: Delete an inet.hh accessor which is unused and makes gcc 9 upset.

This accessor will return a pointer to an unaligned uint32_t. Since
it's not used and it's not clear how to fix it trivially, this change
just deletes it.

Change-Id: I08bc62276d639cc728411f3a8a23be385000ebab
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/24925
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Maintainer: Jason Lowe-Power <jason@lowepower.com>
Tested-by: kokoro <noreply+kokoro@google.com>

src/base/inet.hh

@@ -352,7 +352,6 @@ struct IpOpt : public ip_opt
     uint16_t mtup() const { return ntohs(opt_data.mtu); }
     uint16_t mtur() const { return ntohs(opt_data.mtu); }
     void tr(ip_opt_data_tr &tr) const;
-    const uint32_t *addext() const { return &opt_data.addext[0]; }
     uint16_t rtralt() const { return ntohs(opt_data.rtralt); }
     void sdb(std::vector<uint32_t> &vec) const;
 };