TRX: Remove bogus extern global variable declarations
TRX: Remove bogus extern global variable declarations

Those global variable declarations for non-existing variables were
introduced in 8a8d73a691c709403be4adbe8f2a7150b4d5998a, let's remove
them again.  The source / destination IP address is a parameter of the
phy_link, and not a global variable.

Related: OS#1848
Change-Id: I94b5f934fc3bd00b0467d90029d3053b16594186

osmocom/osmo-bts,osmocom/osmo-bts,osmocom/osmo-bts