MINOR: chunk: inline alloc_trash_chunk()

This function is responsible for all calls to pool_alloc(trash), whose
total size can be huge. As such it's quite a pain that it doesn't provide
more hints about its users. However, since the function is tiny, it fully
makes sense to inline it, the code is less than 0.1% larger with this.
This way we can now detect where the callers are via "show profiling",
e.g.:

       0 1953671           0 32071463136| 0x59960f main+0x10676f p_free(-16416) [pool=trash]
       0       1           0       16416| 0x59960f main+0x10676f p_free(-16416) [pool=trash]
 1953672       0 32071479552           0| 0x599561 main+0x1066c1 p_alloc(16416) [pool=trash]
       0  976835           0 16035723360| 0x576ca7 http_reply_to_htx+0x447/0x920 p_free(-16416) [pool=trash]
       0       1           0       16416| 0x576ca7 http_reply_to_htx+0x447/0x920 p_free(-16416) [pool=trash]
  976835       0 16035723360           0| 0x576a5d http_reply_to_htx+0x1fd/0x920 p_alloc(16416) [pool=trash]
       1       0       16416           0| 0x576a5d http_reply_to_htx+0x1fd/0x920 p_alloc(16416) [pool=trash]
2 files changed