nokia: rename BTS model from nokia_site to nokia-e1
When Nokia BTS support was introduced into Osmocom in 2011, only {Metro,Ultra,In}Site family was supported, and the name of this BTS model in OsmoBSC was set to nokia_site. However, we now also support Flexi Multiradio in E1 Abis configuration with the same code, automatically applying Site-specific or Flexi-MR- specific handling based on the type code returned by the BTS itself - hence calling the BTS model nokia_site and referring strictly to *Site in docs and vty help is now misleading.
At the same time, these newer BTS models support both E1 and IP Abis options, and there is a desire to support IP Abis operation at some point in the future. When/if Nokia IP support becomes a reality, we will certainly need to know upfront which type of Abis we are working with, similarly to how we currently distinguish upfront between E1 and IPA types of BTS. Therefore, the new BTS model name is set to nokia-e1, rather than just "nokia", with the expectation that we will also have nokia-ip in the future.
bts_nokia_site.c source file name is deliberately left unchanged. Source file renames make it difficult to follow changes, hence a slightly outdated source file name is deemed to be a lesser evil. This source file may also be split in the future as Nokia BTS support code grows.
